Why This Matters
Every WaterCompass flow monitor must be matched to the pipe size and material of you water supply line. Providing accurate pipe measurements ensures your flow monitor is properly calibrated and delivers reliable usage data from day one.
What You'll Need
You only need one of the following tools. Choose whichever you have available.
- Digital caliper - most accurate method
- Tape measure or ruler (with inch markings) - good alternative
- A piece of string, a marker, and a ruler - works when other tools are unavailable
Choose Your Measurement Method
Which method should I use?
- Do you have a digital caliper? → Use Method 1 (most accurate)
- Do you have a tape measure or ruler? → Use Method 2
- Do you have a string, marker, and ruler? → Use Method 3
Where to Measure?
Always measure on a straight, exposed section of pipe. Do not measure at joints, fittings, elbows, or threaded connections, as these areas are wider than the pipe itself and will give inaccurate readings.
Method 1: Digital Caliper (Preferred)
A digital caliper is the easiest and most accurate way to measure a pipe. It displays the measure on a digital screen, eliminating guesswork.
- Open the caliper jaws wide enough to fit around the pipe.
- Place the jaws around the outside of the pipe on a straight section.
- Close the jaws until they are snug against the pipe. Do not over-tighten.
- Read the measurement displayed on the screen. Record this number in inches.
Please use the Pipe Size Reference Tables below to determine your nominal pipe size.
Method 2: Tape Measure or Ruler
If you do not have a caliper, you can measure the diameter of the pipe with a tap measure or ruler. This method requires a little more care, but the common pipe sizes are different enough that you should be able to identify yours.
- Hold the tape measure or ruler flat against the pipe so it crosses the widest point (the center).
- Read the measurement across the outside of the pipe from one edge to the other.
- Record the measurement in inches. It is okay to round to the nearest 1/8th inch.
Tip: If the pipe is mounted flush against a wall and you cannot get a tape measure across it for accurate measurement, use Method 3 (String) instead to measure the circumference.
Please use the Pipe Size Reference Tables below to determine your nominal pipe size.
Method 3: String Measurement
If you do not have a caliper or cannot fit a ruler across the pipe, you can measure the circumference (the distance around the pipe) using a piece of string.
- Wrap the string snugly around the pipe at a straight section. The string should be flat against the pipe with no gaps or overlap.
- Mark the string with a marker at the point where it meets the starting end.
- Remove the string and lay it flat against a tape measure or ruler.
- Measure the distance from the end of the string to your mark. Record this number in inches.
Please use the Pipe Size Reference Tables below to determine your nominal pipe size.
Pipe Size Reference Tables
Find the row where your measurement is closest. The value in the Nominal Pipe Size column is the size you will report to HydroPoint.
Which Table Should I Use?
- Copper pipes are metallic with a reddish or green-tinged surface.
- CPVC pipes are typically cream or light yellow rigid plastic.
- PEX pipes are white or gray rigid plastic, often with printed markings.
- PVC pipes are white or light gray rigid plastic, often with printed markings.
If you are unsure of your pipe material, refer to How to Determine Pipe Material before using these tables.
Copper, CPVC & PEX Pipe Sizes (CTS - Copper Tube Size)
Nominal Pipe Size |
Outside Diameter |
Approximate Range |
Circumference Measured |
½" |
0.625" (5/8") |
0.58" - 0.68" |
1.96" |
¾" |
0.875" (7/8") |
0.83" - 0.93" |
2.75" |
1" |
1.125" (1-1/8") |
1.08" - 1.18" |
3.53" |
1-¼" |
1.75" (1-3/8") |
1.33" - 1.43" |
4.32" |
1-½" |
1.625" (1-5/8") |
1.58" - 1.68" |
5.10" |
2" |
2.125" (2-1/8") |
2.08" - 2.18" |
6.68" |
2-½" |
2.625" (2-5/8") |
2.56" - 2.68" |
8.25" |
3" |
3.125" (3-1/8") |
3.08" - 3.18" |
9.82" |
PVC Pipe Sizes
Nominal Pipe Size |
Outside Diameter |
Approximate Range |
Circumference Measured |
½" |
0.840" |
0.79" - 0.89" |
2.64" |
¾" |
1.050" |
1.00" - 1.10" |
3.30" |
1" |
1.315" |
1.27" - 1.37" |
4.13" |
1-¼" |
1.660" |
1.61" - 1.71" |
5.22" |
1-½" |
1.900" |
1.85" - 1.95" |
5.97" |
2" |
2.375" |
2.33" - 2.43" |
7.46" |
2-½" |
2.875" |
2.83" - 2.93" |
9.03" |
3" |
3.500" |
3.45" - 3.55" |
11.00" |
Understanding “Nominal Pipe Size”
Nominal pipe size is an industry-standard label. It does not match the actual outside diameter of the pipe. For example, a pipe labeled “1 inch” actually measures 1.25" (copper) or 1.315" (PVC) on the outside. This is why measuring is necessary - you cannot simply look at the pipe and guess.
What if I'm Not Sure?
If any of the following apply, contact HydroPoint for assistance:
- Your measurement falls between two sizes on the table.
- The pipe is covered by insulation, paint, or a wall and you cannot measure it directly.
- The pipe material does not match any of the description above.
- You are not confident in your measurement.
A photo can help
If you are unsure, take a photo of the pipe next to the form of measurement, like the tape measure, and send it to your HydroPoint representative. This can often be enough for our team to identify the pipe size and material remotely.
Next Steps
- Once you have both your pipe size and pipe material, provide this information to your HydroPoint representative or enter it during the site readiness process.
If you have questions or need help at any point, contact HydroPoint support at 800-362-8774.
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