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What Size Is Toilet Water Supply Line? (Quick Answers)

Water supply lines of different places might have different sizes. Well, a bathroom and a kitchen water line size also differ though they are in the same home. Moreover, the whole water line size of the house connects all the water lines together to the main water tank. The sizes would vary accordingly.

Following the below tips and information regarding the water supply line in the toilet and its size of it would help you to install one.

What size is toilet water supply line? 

Toilet water supply line has a common diameter of ⅜ inch. You can also use ½ inch though it’s not necessary. The toilet water supply line provides enough water with the pressure for the flush process. You can take a water supply line of any length as long as it fits the length of the shutoff valve. 

A house can have different water lines. Not all the water lines are of the same size. The size varies with the place where you are using the water lines. Even the connection to the main water line should also be considered while choosing the size of the waterline.

Moreover, a kitchen water supply line and a toilet water supply line can not be of the same size. The size would vary here as well. 

A kitchen would supply water with a certain pressure. The same goes for the toilet water supply line. Mostly ¾ is the suitable one for the kitchen water supply line, unlike the toilet water supply line. 

A toilet supply line is required for the flush process. You need to put sufficient pressure on the water so that the wastage gets flushed. Otherwise, there is no use in placing flush. The water supply line of ⅜ inch diameter is suitable to put enough pressure.

The shut-off valve compression pressure is also ⅜ inch. Well, the standard size is more like up to ½ inch. You can also put a ½ inch water supply line in the toilet. But it is not needed. Placing the standard size of the toilet water supply line is better. 

As the water supply line lasts for years, you should choose the right one. You can also bend the water supply line. The length of the toilet water supply line is not limited to any fixed number. Rather you can put any length of toilet water supply line as long as it fits. 

What is the standard water supply pipe size?

The main water supply line pipe is always either ¾ inch or ½ inch. It is the diameter of the pipe. Well, the length does not even matter here. 

You can choose any length of pipe. The branched pipes can also be of the same diameter. But the water supply pipe for individual room wood varies in size.

You can easily go with putting a pipe of ¾ inch in anywhere in the house. But the diameter should be of minimum limit so that the water can flow through the pipe. 

Otherwise, the water will stand still in the pipe with no flow. A toilet water supply line pipe can have a diameter of ⅜ inch to the least.

Meanwhile, the shower, bathtub, and kitchen sink can have a ½ inch water supply line. Less than the standard diameter of each purpose would reduce the water pressure. Well, the size also depends on the number of fixtures. 

Is 3 inch pipe OK for toilet water supply? 

It is not exactly necessary to use a 3-inch pipe for the toilet water supply. A toilet water supply would need a pipe size of ⅜ inch or ½ inch in diameter. You can choose a 3-inch long pipe for the toilet water supply. 

Moreover, the 3-inch pipe has particular use on the toilet. But it is not exactly suitable for the toilet water supply pipes. 

A 3-inch pipe is generally used for the drainage mechanism of the toilet. The wastage is moved out of the toilet through the drainage. 

The pipe can be 3 to 4 inches in that case. In the case of the toilet water supply line, 3 inches is a bit too wide. It can give more pressure on the water. But it’s better to keep it minimal. 

Are toilet and faucet supply lines the same?

The toilet and faucet supply lines are quite the same in size. Both are of ⅜ inches and connect to the water valve. 

Well, the compression fitting is also ⅜ in both cases. But there is a difference in connecting the faucet supply lines and toilet water supply lines. The faucet line mainly consists of connectors of different sizes. 

Though the pipes can be of the same size, the difference in connection to water lines with the toilet supply line and faucet supply line is very different. Moreover, the faucet supply line should not be less than ⅜ inch in size. 

You can increase it up to ½ inch only. Yet, there is no guarantee that ½ inch would work without any trouble. 

What type of pipe is used for the toilet water supply line?

Water supply lines are fixed in order to give enough water flow throughout the house. And also through all the water supply lines. 

The main water line can be of a different material than the branched or connector water lines. The following are the types of pipes that are mostly used as the toilet water supply line.


The most common type of pipe used for faucet lines and toilet water supply line is PVC. It is suitable for high-pressure water. Well, the pipes used in the water line should be able to withstand high pressure and temperature changes.

PVC is also strong and the amount is in the range. Moreover, it is more suitable for drainage pipes. 


The PEX pipe is one of the most commonly used pipes at this time. Many prefer it over old pipes made of copper or PVC. You can stretch it and also bend it. It is quite flexible to put. As a result, it becomes easier to install the PEX pipe.

Apart from that, the cost of it is not even high. If you want to put it in the toilet line, there is no need to worry. But you can not put the pipe in a place where it is exposed to the sun. 


It is the modified version of the PVC. Well, it is also suitable for the water supply line in the toilet. 

It can last for a long time and is not affected by bacteria or mold. Apart from that, it is also easy to install. It can withstand both hot and cold water. And also have enough protection to be able to flow high-pressure water.


Some may also use copper pipes for the water supply line. It is suitable as it prevents corrosion and the high water pressure can not damage the pipe at all. It is likely to last for a longer time. Still, it is too costly in comparison to other pipes. 

How to measure toilet water supply line?

The measurement of the toilet supply line can be done by keeping some things in consideration. All the water supply line size is decided by several factors. 

It is no different for the toilet water supply line. You can follow below to measure the toilet water supply line while keeping certain factors in consideration. 

Measure water supply line:

The toilet water supply line can be measured with a tap. The length can be measured or guessed. 

A toilet mostly needs a smaller length water supply line as too long lines would look bad. You can install up to 12 inches of the water supply line. More than this length would seem inappropriate.

The diameter stands the same as the standard. You can go with ⅜ inches diameter which would be connected to the water valve or the compression fitting. Well, it is necessary to measure the length beforehand as long pipes are not appreciable. 

Final Thoughts

Overall, the toilet water supply line is mainly of ⅜ inch to 1/2 inch. The compression fitting is mostly of ⅜ inch whereas the outlet size is ½ inch. You can choose the water supply line to be as long as you want. But too much bending and twisting of the pipe might not be a good decision.