Tips to Measure and Install Plumbing Pipes

If you want to install or replace your home’s plumbing, it’s essential that you get the measurements right. Whether you’re fixing a single pipe or adding to your current system, doing the work upfront will save you a lot of time and frustration moving forward. Here are some tips to measure and install your plumbing pipes.

Measure Current Pipe Sizes

If you’re new to plumbing, navigating pipe sizes can be overwhelming. You’re not just working with the outer diameter of the pipe, as you may think. It’s actually the nominal diameter, which requires a conversion to nominal pipe size (NPS).

How to Measure Your Plumbing Pipes

If you’re replacing your existing pipes, you can measure them to ensure you have the right numbers. All pipes will have the NPS printed on the pipe itself or a label.
  There are three ways you can measure and convert your plumbing pipe sizes on your own.

Direct Diameter Measurement

If you have access to the end of your pipe, you can measure the direct diameter with a measuring tape or ruler. Just put it across the open end of the pipe in the center. The only downside of this method is that it can be easy to measure a little off center, leading to incorrect numbers.

Outside Diameter Measurement

If your pipes are already installed and you don’t have an end to measure, you may need to measure the outside diameter. Pipe calipers measure the diameter of the pipe from the outside accurately, and they’re easy to use.

Circumference Measurement

The circumference is an easy measurement to take, but then you need to perform a calculation to get the outside diameter. Wrap flexible tape or a string around your plumbing pipe. Record the measurement where the tape overlaps. If you’re using string, mark where the string overlaps, unwrap it, and measure it. Divide this measurement by pi to get the outside diameter. Pi = 3.1415 Circumference/Pi = Outside Diameter Then, use the charts to find the NPS.

Nominal Diameter Conversion Chart

(All Measurements in Inches)
  Outside or Inside Diameter Decimal Equivalent Nominal Diameter Typical Threads Per Inch
5/16 0.313 1/16 27
13/32 0.405 1/8 27
35/64 0.540 1/4 18
43/64 0.675 3/8 18
27/32 0.840 1/2 14
1-3/64 1.050 3/4 14
1-5/16 1.315 1 11-1/2
1-21/32 1.660 1-1/4 11-1/2
1-29/32 1.900 1-1/2 11-1/2
2-3/8 2.375 2 11-1/2
2-7/8 2.875 2-1/2 8
3-1/2 3.500 3 8
4 4.000 3-1/2 8
4-1/2 4.500 4 8

Tips for Pipe Installation

The measurements for your plumbing job are a big part of the process. Then, you have to consider your materials to make sure the job is done right.  

Use PEX Pipes for Installation

PEX pipes are convenient for replacing only one pipe. PEX is a type of plastic that cuts easily, is flexible, and merges into existing plumbing easily. It only requires simple fittings, even if you’re matching it to a different material. PEX is also affordable compared to steel or copper.

Get the Correct Size

All the components of your plumbing system have specific pipe sizes. Make sure your measurements are correct and compliant with local plumbing codes to ensure you’re using the right size.

Match Pipe Materials

If you’re using different pipe materials for your new pipes vs. your existing pipes, you could end up with fit issues, premature corrosion, or worse, a leak or burst pipe. Make sure your new pipe materials match your current pipe materials, or if you must, use the right fittings to bring everything together.

Check Your Fittings

You may need to tie together different pipe materials with transition fittings. Pipe fittings connect your pipes and redirect the water flow. Specific fittings are designed for different pipe materials, such as PEX for water line fittings or PVC and ABS plastic for waste and drain fittings. Sometimes, you may need to tie together different materials with transition fittings. There are plenty of different fittings, couplings, adapters, and more, ensuring that different materials are cohesive and direct the water where you want it to go. For example, bend fittings have different degree angles to make the pipes fit into the space in your walls, floors, or ceilings. Wyes or double wyes prevent backflow, which is important when you’re dealing with waste drainage.

Dry Fit Pipes Before Attaching Them

The rule is “measure twice, cut once.” The same applies to your plumbing pipes. Always check your pipes and fittings with a dry fit, which is when you put the pipes together without adhesive to make sure they fit properly. If you attach your pipes and fittings without paying attention, you could end up with a much bigger job having to take it all apart before you can continue. Would you prefer to hire a professional for your plumbing? Contact the pros at Moore Home Services to schedule your appointment!