# Calculating the required water supply line size (2023)

The water line size is vital to providing adequate volume of water to the occupants of a building. There are three main factors that determine the correct water supply line size, which is also referred to as the water service line. The three factors are as follows:

1. Plumbing fixture count: A calculation using all of the plumbing fixtures in a building.
2. The length of the run of pipe: The distance from the main inside control valve to the connection on the city water main.
3. Classification of the building: Residential and Commercial buildings have different sizing requirements.

## Some water supply line size facts simplified

Increasing the water supply line size to just one pipe size larger makes a dramatic difference. What individuals that are not in the plumbing trade do not realize, is that understanding length and understanding area are quite different factors from each other.

As an example 1 1/4″ is only 25% larger than 1″. But in terms of area, the inside area of these size pipes (water supply tubing) is a difference of about 56% greater. As another example let’s compare 1 1/2″ pipe to 2″ pipe. The difference in area inside an 1 1/2″ pipe compared to a 2″ pipe is around 77%.

(Video) Water line sizing

In terms of the DEP water supply line size table, whose key component is gallons per minute, the differences are even more dramatic. Basing calculations of an average run of pipe of 50′, an 1 1/4″ line provides 16 gallons per minute. On the other hand a 1″ line only provides 9 gallons per minute. Therefore an 1 1/4″ line provides almost 77% more gallons per minute than a 1″ line.The gallon per minute calculations on the DEP sizing table are also based upon some other vital assumptions. All flow calculations are based upon connecting to the proper size of tap connection on the city water main. They are also based upon the building being on level ground. As an example, a house located on a hill or raised ground will decrease the flow rate.

What does all this mean to the average property owner? It means that for a nominal amount of money, increasing the size by just one size of water supply line provides dramatic benefits. The photo below clearly illustrates this point. But it should also be noted that if the inside plumbing on a building is undersized, no benefit will be derived by increasing the service line size unless the inside plumbing is also increased as well.

### What water supply line size is typically required?

A typical one family house is supplied by a 1″ water service line. A one family house typically has the following plumbing fixtures present:

• Kitchen sink
• Laundry tray
• Dishwasher
• Washing machine
• Full bathroom
• An outside hose connection.

A two family house can virtually never size out for a 1″ service line. The only exception would be the extremely odd case of a city water main being located under the public sidewalk. The house would have to have no front yard whatsoever; which would result in only a 15′ run of pipe. Obviously this is a very uncommon and rare situation.

(Video) Sizing A Water Main: Use Our Free Water Line Size Calculator Service

In the case of a three family house an 1 1/2″ service line is typically required. Again the exception would be if the length of the run of pipe was only 35′ or less. In most cases a six family house or greater will require a 2″ water service line.Every type of plumbing fixture has an estimated gallons per minute factor. All of the plumbing fixtures inside a building combine to factor into the required water service line size for the building.

### Cases vary in determining the proper water supply line size

The actual reality that exists is that most older buildings, those built prior to 1990 or so, will frequently have lines smaller than suggested above. In many cases this results in no ill-effects, as the NYC DEP sizing table is very conservative. However each case will vary. As an example, in some neighborhoods there are six family homes served by lead water service lines smaller than 1″. In extreme cases like this the water pressure drops, and inadequate volume are normal everyday issues for the occupants. Remember, even if you’ve gotten used to it, a pressure drop when using water in your home is not normal. No home or property was designed for this to happen.

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### Sizing tables differ for residential and commercial properties

The sizing table differs dramatically for a commercial property as compared to a residential property. There is good reason for that. Among the chief reason is that a plumbing fixture typically gets used much more frequently in a commercial space. As an example a sink in a one family house is used sparingly as compared to a sink inside a busy restaurant.

Fixture count is the gallons per minute value each plumbing fixture is attributed in the sizing table. As an example the DEP sizing table sinks, dishwashers, and washing machines are attributed a fixture count of 4. While like residential plumbing fixtures have exactly 1/2 that fixture count. As a result the DEP sizing table, commercial properties typically require much larger water service lines than residential properties to meet code.

(Video) What size water main does your home require? How to determine

### Why the length of the run is a factor

Part of supplying water to a building is based upon pressurized water passing through the water supply line. The line itself provides resistance to the water flow. Therefore the length of the run is a major factor. The longer the run, the less gallons per minute can flow through the service line.

Length of run actually has a dramatic affect on the supply capabilities of each water service line size. As an example the typical water service line will lose approximately 33% of its water delivery capability when the length of the run is increased from 30′ to 60′. As a specific example an 1 1/4″ line can deliver approximately 21 gallons per minute over a 30′ run, yet only approximately 14 gallons per minute over a 60′ run.

While the length of run is a major factor for all water supply line size calculations, it becomes more of factor when the run is unusually long. When a building has a large set-back from the property, or is on w very wide roadway, it is easy to overlook the this factor. In cases where there is a long run it would be an error to base the water supply line size strictly on the fixture count.

## Typical signs of inadequate water volume or water pressure

Occupants of a building may have longstanding issues with insufficient water volume or pressure, and accept it as normal. It should be understood that water pressure and water volume are two separate and distinct issues. Water pressure is the force that water flows from a plumbing fixture. Water volume is the amount of water present to service an entire building.

Three typical issues that result from volume or pressure problems are as follows:

(Video) Plumbing Supply Line Sizing

1. Water temperature changes when water is used in the building, such as a toilet being flushed.
2. Loss of water pressure when a shower or washing machine is being used.
3. Change in water pressure or volume when a lawn sprinkler system kicks on.

Water pressure and volume issues and solutions can be complicated. Frequently they do not involve the water supply line size, but other issues are the cause. It is always best to trust a Licensed Master Plumber to investigate and resolve plumbing issues like these. Only a skilled and licensed plumber will have the knowledge and expertise to provide a correct and cost effective solution.

## Master Plumber Paul R. Balkan explains sizing water lines

Paul R. Balkan is the President of Joseph L. Balkan Inc. He is an expert in the field of house sewer and water service line work. Here are some of his insights concerning water pressure and sizing issues.

There are several factors involved in getting adequate water flow out of the plumbing fixtures in a building. Water pressure is usually measured as pounds per square inch. When no water is being used in a building, and assuming there is no pumps or roof tanks, or other devices being used, the maximum height that water can rise in a building is determined by the pressure in the City Water Main.

One psi (pound per square inch) will raise water vertically 2.31 feet. If the pressure in the City water main is 40 psi the water will raise a maximum of 92.4 feet vertically above the City water main. It is important to realize that this is not affected by the size of the pipes.

The size of the pipes becomes important when water is being used in the building. The larger the diameter of the supply pipes the less of a pressure drop will occur as more and more plumbing fixture are used at the same time.One way of looking at it is to imagine the size of the supply pipe as being like a valve. If you were to connect a garden hose to a fire hydrant and barely open the hydrant valve, the equivalent to having a small supply pipe, the water coming out of the hose might go 30’.

(Video) Water Supply Pipe Sizing Using Plumbing Charts

On the other hand, without adjusting the valve, disconnect the garden hose and connect a fire hose instead. This is similar to having a lot of plumbing fixtures attached to an undersized water supply. The water might then only go 1-2’. Opening the valve all the way, equivalent to a large supply pipe, and the pressure of the water coming out of the hose could knock somebody over. Nothing changed in the City water main supplying the hydrant, just the size of the passageway that the water had to go through. Naturally this is a thought exercise, and fire hydrants should not be tampered with!

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## FAQs

### How do I calculate the size of my water supply line? ›

The 75% Method means that if there's both a hot water and cold water supplied to the fixture, we take that total fixture unit and multiply it by . 75. The resulting number is the size of the each branch.

Is 3 4 water line enough for a house? ›

3/4 supply is good for most houses. If you have low pressure with taps on 3/4 may be small. If you have big house with many lavatories and people 3/4 may be small.

What size is a typical water supply line? ›

The most common pipe diameter for water mains is 6 to 16 inches, with 8, 10, and 12 inches also being used. Branch lines providing service to individual homes, offices, buildings, and businesses vary in size from as small as half an inch in diameter up to 6 inches.

What is the thumb rule for pipe sizing? ›

A rule of thumb that incorporates pipe size is to choose liquid lines to handle a velocity of 1.5 +d/10 where “d” is the pipe diameter, inches. This gives 1.6 m/s for 1-inch and 2.5 m/s for 10-inch piping, and about 20 kPa/100 m pressure drop.

Whats better 1 2 or 3 4 water line? ›

IIRC, a 3/4" diameter line holds twice the volume of a 1/2" diameter line. Use a cheap crimp fitting in there and you have all that extra water volume and a reduced flow. Use a 1" trunk and branch system and you may as well put the kettle on.

Is 3/4 PEX big enough for main water line? ›

It's a good idea to install 1/2-inch or 3/4-inch PEX for your main lines for adequate water flow. When replacing old water supply lines with PEX the standard is to use the same size plumbing, although you can transition from 3/4-inch to 1/2-inch plumbing with an adapter.

How many GPM can you get through a 3/4 pipe? ›

Water Flow (GPM/GPH) based on Pipe Size and Inside/Outside Diameters
Assume Average Pressure (20-100PSI). About 12 f/s flow velocity
3/4"0.75 - 0.85"23
1"1 - 1.03"37
1-1/4"1.25 - 1.36"62
1-1/2"1.5 - 1.6"81
9 more rows

How much water can a 1-inch line flow? ›

Here are the average water flow rates based on typical municipal water lines: ½-inch pipe: 50 gallons per minute. ¾-inch pipe: 110 gallons per minute. 1-inch pipe: 210 gallons per minute.

What is the minimum size pipe that can be used on a water column connection? ›

The water column drainpipe and valve shall be not less than ¾-inch pipe size.

What is the most common water supply line? ›

This is the most common type of used water line today. It is a type of plastic composite material that comes in a variety of colours. Typically, since the colour choices are so vast, you will get some sort of red for hot water lines, and blue for cold water lines.

### What is line sizing criteria? ›

When sizing lines the sizing criteria shall be minimum life cycle cost, this may include evaluation of functional requirements, cost of piping, weight, CO2-tax, energy costs, mechanical and process limitations, expected lifetime of piping, maintenance cost etc.

Does pipe size affect water flow? ›

Larger pipes increase the water flow through the line, but if the water isn't up to that necessary flow, it won't increase your water pressure. Municipal water systems have impressive pressure, but that doesn't mean a larger line can help. Bigger lines do not always help things get faster o stronger.

What is the ideal pipe velocity for water? ›

What is a 'good' pipe velocity? An installation engineer chooses pumps and sizes pipework to achieve a satisfactory pipe velocity. For water-like liquids with no entrained solids (for example: chemicals, paints, petrol, beverages), a pipe velocity of about 1 – 2 m/s is considered an acceptable value.

What happens if you over tighten water supply line? ›

Screwing a supply line on too tight is one of the worst things you can do. Such overtightening will cause the metal threads inside of the line to become warped, making it much easier for water to slip past. It may also damage the rubber O-rings inside of the line.

How many inches apart should water supply lines be installed? ›

Hot and cold water lines should be approximately 6 inches apart unless the hot water line is insulated. This is to ensure that the cold water line does not pick up heat from the hot water line [2]. The supply mains should have a drain valve stop and waste valve to remove water from the system for repairs.

What happens when you reduce water pipe size? ›

In a fluid passing through a pipe, a reduction in the diameter of the pipe can compress the flowing fluid. It flows faster, which increases the flow rate. And if the diameter increases, then the flow rate reduces.

Is PEX better than copper for water lines? ›

PEX pipe is not only cheaper than copper but more durable too. PEX is immune to corrosion and mineral build-up, and it's not affected by electrolysis, which can cause small pinhole leaks in copper piping. Copper pipes can last anywhere from six months to the life of a building.

Does water line size affect pressure? ›

So, will bigger pipes increase water pressure? The short answer: yes and no. Larger pipes will increase the amount of potential water flowing through the line. However, if the water isn't up to that necessary flow rate, it won't increase water pressure.

Is PEX or PVC better for water lines? ›

When a connection to copper or other metal pipes is required, PEX works better than PVC because crosslinked polyethylene won't corrode. - Price. When you compare the material costs of PEX vs PVC, PEX comes out more expensive. (However, balance this factor against the lower labor cost to install PEX.)

How much PEX do I need calculator? ›

Your vehicle's recommended tire pressure can typically be found on a sticker inside the driver's door. It's also usually listed in the owner's manual, says Cars.com. Tire pressure is measured in pounds per square inch (psi). You may also notice that the sidewall of the tires lists a tire pressure.

### How do I know what size PEX pipe to use? ›

The larger the distance from the manifold to the tube fixture, the wider the PEX pipe should be. You can opt for a ⅜-inch line for lengths up to 250 feet. If you want to adequate water pressure up to 350 feet, opt for a ½-inch line. A 500-foot line will work better with a ¾-inch PEX tubing system.

Should I use 3 4 or 1 inch PEX? ›

PEX tubes range in diameter from 3/8-inch to 1-inch for residential applications. For adequate water flow, it's a good idea to install 1/2-inch or 3/4-inch PEX for your main lines. The standard when replacing old water supply lines with PEX is to use the same size.

How many gallons of water can a 4 inch pipe handle? ›

STEP 3: Choose the number of drainage zones.
Pipe SizeMaximum Flow Capacity
3″44.0 GPM
4″75.0 GPM
6″175.0 GPM

How many GPM can a 6 inch pipe have? ›

97) for flow going through Flexible PVC Pipe.
...
Water Flow Chart #3.
Size (ID, inches)Length (inches)Flow (GPM)
615.505400
8 more rows

How do you calculate flow capacity of a pipe? ›

Example of How to Calculate Pipe Volume
1. For a 1-inch pipe that measures 50-feet long:
2. radius = 1 inch ÷ 2 = . 5 inch. length = 50 × 12 inches = 600 inches. volume = π (pi) × radius squared × length. volume = 3.14159 × (. 5 x . 5) × 600. volume = 3.14159 × . 25 × 600. volume = 471.24 in³

How much water does a 1 inch line hold per foot? ›

Each 1-1/2-inch ID x 100-foot hose length holds 9 gallons. Each 1-inch ID × 100-foot hose length holds 4 gallons.

How many GPM can a 1 2 hose flow? ›

A 25-foot, 1/2-inch diameter hose attached to a faucet that supplies water at 40 psi has a flow rate of 24 gallons per minute, while a 100-foot hose only has a flow rate of 6 gallons per minute.

How do you calculate minimum pipe size? ›

The equation for pipe diameter is the square root of 4 times the flow rate divided by pi times velocity. For example, given a flow rate of 1,000 inches per second and a velocity of 40 cubic inches per second, the diameter would be the square root of 1000 times 4 divided by 3.14 times 40 or 5.64 inches.

What are the 3 factors to be considered in determining the size of the pipes required for sizing supply lines? ›

Three Steps to Sizing Plumbing Piping Systems
• Add up the total number of water supply fixture units (wsfu) required in the facility.
• Estimate demand using the table from the IPC that correlates wsfu to expected demand.
• Size the pipe using demand vs. friction loss curves found in the IPC charts.
Jan 5, 2016

What is the minimum supply pipe size to a modern dwelling? ›

Connection size

For most domestic properties a standard 25mm or 32mm connection will be sufficient. For larger commercial properties you may require a bigger supply - this will be based on the fittings e.g. toilets, basins, showers etc you're planning on installing in the property.

### Are all water supply lines the same size? ›

The two most common are 3/8- and 1/2-inch compression or male pipe thread. Faucets connectors aren't completely standardized, but most have 1/2-inch male pipe thread connectors.

What type of pipe is not recommended for water line? ›

Avoid using polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC). These pipes contain the highest levels of chemicals of concern and they are typically installed using hazardous solvents.

How much water can a 1 inch line flow? ›

Here are the average water flow rates based on typical municipal water lines: ½-inch pipe: 50 gallons per minute. ¾-inch pipe: 110 gallons per minute. 1-inch pipe: 210 gallons per minute.

Does increasing pipe size increase water pressure? ›

So, will bigger pipes increase water pressure? The short answer: yes and no. Larger pipes will increase the amount of potential water flowing through the line. However, if the water isn't up to that necessary flow rate, it won't increase water pressure.

Will increasing water line size increase pressure? ›

Larger pipes increase the water flow through the line, but if the water isn't up to that necessary flow, it won't increase your water pressure. Municipal water systems have impressive pressure, but that doesn't mean a larger line can help. Bigger lines do not always help things get faster o stronger.

What is the best way to measure a line? ›

Generally, we measure a line segment with the help of a scale which has marking in centimetres (cm) and inches (in). Mostly we measure the line segments in centimetres. Each centimetre is divided into 10 small equal parts, called millimetres (mm).

How do you calculate flow rate from pipe size? ›

The equation for pipe diameter is the square root of 4 times the flow rate divided by pi times velocity. For example, given a flow rate of 1,000 inches per second and a velocity of 40 cubic inches per second, the diameter would be the square root of 1000 times 4 divided by 3.14 times 40 or 5.64 inches.

How do you measure tubing size? ›

Tubing is measured by the OUTSIDE DIAMETER (O.D.), specified in inches (e.g., 1.250) or fraction of an inch (eg. 1-1/4″). Pipe is usually measured by NOMINAL PIPE SIZE (NPS).

## Videos

1. Does Size Really Matter? - Water Supply Pipe Flow Rates
(gregvancom)
2. How to Determine Your Supply Line Size
3. How to Size Your Water Lines (PEX & Copper)
(Williams Plumbing & Heating)
4. Choosing the size for your water supply line
(PEX Universe)
5. Supply Line Sizes for Toilet and Faucet
(FIX IT Home Improvement Channel)
6. Water supply demand (GPM) calculation, plumbing system design as per IPC standard, booster pump
(MEP Engineering Tutorials)
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