How to Calculate Equivalent Pipe Length for Fitting

Use a tape measure to calculate the new pipe section's length.

There are different types of pipes found in household construction, the most frequently used being sewer pipes -- usually either PVC or ABS hard plastic -- water supply pipes -- either CPVC or copper -- and black coated hollow steel gas supply pipes. If a section of pipe has cracked or has attained damage, that section has to be cut out and a new equivalent pipe length section made to replace it. Though the process of cutting out the damaged section varies depending on what type of pipe it is, calculating the equivalent length of the new section is the same process.

Things You'll Need

• Tape measure
• Fine marker pen

Instructions

1. Measure and mark the pipe six inches on each side of the damaged area. A hand saw or circular saw is used to make a straight cut through the pipe at the marks on each side of the damaged area with PVC and ABS sewer pipe, a tube cutter quickly cuts through CPVC water pipe and a tubing cutter cuts through both copper and steel gas pipe.

2. Measure the distance between cut pipe ends on the existing pipe. Do not measure the section of pipe that has been cut out, as the damaged area may have stretched that section of pipe and therefore reflect an inaccurate measurement.

3. Measure and mark the new pipe to the same calculated measurement. Use the same tool to cut through the pipe as you did to remove the broken pipe section. If cutting PVC or ABS sewer pipe, scrape off any burrs from the cut pipe end using a utility knife. If working on gas pipe, chances are the required pipe length will not be exactly the same size as "off the rack" gas pipes in the store. However, major DIY chains can both cut to length and thread the ends of any required gas pipe you need.

4. Hold the new section of pipe between the two existing pipe ends. If cut correctly, the new pipe section should fit snugly between the two pipe ends, with no more than a 1/8-inch gap. Couplings can now be attached to join the new pipe section to the existing pipe ends.

Tips & Warnings

• If installing gas pipe, a union joint has to be fitted between one existing pipe end and the new pipe section. The new pipe section will be measured minus the length of the body of the union joint; that is, the joint length less the length of the inlets on both ends the gas pipe threads into.

References

• This Old House: Gluing PVC Pipe
• Hammer Zone: Cutting PVC Pipe - Various Methods