How To Measure Pipe Diameter

Measuring your main water line diameter is an important step in helping to determine what size of water softener you should buy. The diameter of the water main is important because it helps us to understand the maximum flow that your home can demand, which in turn partially determines the size of system your home needs.

There are a few different ways to measure the diameter of your main line which we'll get to in a moment, but first, it's important that you identify which line it is that you need to measure. This can be different for City dwellers vs. Rural dwellers.

In The City

If you live in a home in a city or town and get your water from the municipal water source, then your main water line enters your home and flows to your water meter. The pipe that you need to measure is the pipe that exits the water meter:

City water main measurement

 

Rural Dwellers

If you live in the country you'll have a different setup than those who live in the city. The typical rural system has this general layout:  Water Source >Pump > Pressure Tank > Distributed to Home. Where the water enters your home usually looks something like this:

rural water main measurement

The graphic above shows that you want to measure the diameter of the water line that exits the pressure tank. This is often a smaller-diameter pipe than the one that enters the pressure tank.

What If You Don't Have A Pressure Tank?

There are an increasing number of homes that are opting for 'constant pressure pump' systems. These systems don't have a pressure tank, which can make the process of knowing which line to measure a little more confusing. In these cases, you simply want to measure the diameter of the pipe that comes into your home before the pipe branches off to the hot water heater.

How To Measure The Pipe Diameter

Once you've identified the pipe that needs to be measured, you have to actually measure it.  There are two good ways to do this:

Option 1 - Caliper Measurement

We include a diameter-measuring caliper in our Softener Prep Kit, or you might have one at home already. This is the quickest and easiest way to measure diameter. Simply open up the caliper, close it on the pipe you want to measure and read the diameter:

how to measure pipe diameter

Option 2 - Use a String

If you don't have calipers, the next best method of measuring the diameter is to use a piece of string to measure the distance around the pipe (circumference) and then convert this to the diameter. Here's a diagram that shows circumference:

pipe circumference

To measure diameter using the 'string method' simply take a piece of string and anchor one end of the string to the pipe using a piece of tape. Wrap the string around the pipe until it meets up with the taped end and mark this length on the piece of string (or cut the string at this point). Then use this formula to convert the string length to get the outside diameter of the pipe:

Length of String / 3.14 = Diameter

It doesn't matter if you use inches or centimetres for the measurement, but you need to know that the resulting diameter will be in the same units that you used to measure the string.

If you'll be using your result in our Water Softener Selector it will want the pipe diameter in inches. If you used centimetres in your measurement you can convert to inches by dividing the result by 2.54

Why Pipe Diameter Matters

Pipe diameter matters because the effectiveness of water treatment equipment depends very much on the flow rate through the equipment. Knowing the diameter of your main water line is the easiest and most accurate way to estimate the maximum flow rate that your home can demand. So by knowing the diameter of your main water pipe, you effectively know the maximum flow rate that your home can expect a piece of water treatment equipment (like a water softener) to have to manage.