Measuring pipe length with fittings accurately is important for proper installation in plumbing, industrial piping, or any system involving pipe connections. Here’s how to do it depending on the type of fittings you’re using:
General Guidelines Before Measuring
Know the type of fittings: Are they threaded, socket-welded, push-to-connect, or flanged? Each type affects length differently.
Understand "center-to-end" and "face-to-face" dimensions: Fittings have standardized lengths that contribute to the overall pipe run.
Always measure to the centerline of fittings unless otherwise specified.
How to Measure with Different Types of Fittings
1. Threaded Fittings (e.g., NPT)
Measure from end to end, including the threads.
If both ends are threaded, subtract the thread engagement (usually ½ to ¾ inch per fitting) to get the true pipe length.
Example: If a threaded nipple connects two elbows, subtract the engaged portion (approx. 1–1.5") from your measurement.
2. Socket Weld or Solvent Weld (PVC/CPVC) Fittings
These fittings overlap the pipe.
Measure the insertion depth of the pipe into the fitting (called socket depth) and subtract it from each end.
Use a depth gauge or caliper to measure the socket depth.
Example: If you’re joining two elbows with a PVC pipe and each socket is 0.75" deep, subtract 1.5" from the total measured length to get the correct pipe cut length.
3. Butt Weld Fittings (Common in Industrial Piping)
Measure from center-to-center of fittings (e.g., elbow to elbow).
Use ASME/ANSI standard tables for fitting dimensions (e.g., center-to-end for elbows, face-to-face for flanges).
Then subtract fitting allowances accordingly.
Example: For a 90° long radius elbow (2" pipe), center-to-end is typically 1.5". If you have two elbows, subtract 3" from the total center-to-center length.
4. Flanged Fittings
Measure face-to-face if connecting two flanges.
Add gasket thickness if it’s significant in your system design.
5. Push-Fit (Quick Connect) Fittings
These have a known insertion depth—check the product specs.
Subtract the inserted portion from your total measured run.
Example – Measuring Pipe with Two Elbows (Butt Weld)
Let's say you're installing a straight pipe between two 90° elbows in a pipeline:
Measure center-to-center between the elbows (e.g., 36").
Look up the center-to-end dimension for your pipe size (e.g., 1.5" per elbow for 2" pipe).
Subtract both fitting allowances: 36" - (1.5" + 1.5") = 33" pipe cut length.
Tips for Accurate Measurement
Use a pipe fitter's handbook or manufacturer’s specification sheets.
Always dry-fit components first if possible.
Use a laser measure or tape measure with clear reference points (pipe centerline or fitting face).
