How to Measure a Sink Drain Drainpipe J Trap & Supply Lines

Kenneth Crawford

When you replace a sink in the kitchen or bathroom, it is a good idea to replace the drain lines and the water supply lines. Just as you take measurements to ensure you purchase the correct size sink, it is necessary to take measurements of the lines to ensure you purchase enough for the project. Measuring a sink drain drainpipe J trap and supply lines does not have to be exact. Drainpipes are sold in longer pieces and will need to be cut down to size. Flexible supply lines are longer than the straightest measurement to ensure there is enough line to connect to the faucet.

  1. Measure from the wall where the house drain pipe is to the nut securing the J trap to the sink drain pipe with a tape measure. Add two inches to the measurement and write it down on a piece of paper. This is the measurement for the rear sink drain pipe. The additional two inches is where the pipe slides into the house wall drain.

  2. Place the end of the tape measure on the top of the nut securing the dink drain pipe to the bottom of the sink basket. This is known as the tailpipe. Measure down to the nut securing the J-trap to the tailpipe and write the measurement down.

  3. Position the tape measure over the end of the nut securing the J trap to the sink wall drain pipe and measure to the front side of the J-trap. Write the measurement down.

  4. Move the end of the tape measure to the top of the water supply line connecting to the faucet. Measure down to the shut-off valve and write down the measurement. Repeat for the remaining water supply line.