How to size a v-belt

V-belts have a multitude of functions in the automotive, agricultural and industrial sectors. V-belts can propel a simple machine or intricate parts of a vehicle, such as the water pump, alternator and air-conditioning compressor. Sizing a V-belt for automotive applications consists of taking a combination of measurements to find the total size or number for your application. You can take measurements for V-belt size in less than 30 minutes---even if you have never attempted this project before.

Open the bonnet of the vehicle you wish to measure for V-belt fit.

Run a string with one hand in the exact routing pattern the V-belt will take when installed. Use your other hand to complete the pattern and connect the end of the string back together with the spool of string. Cut the string to the exact measurement you just mocked up on the pulleys.

Measure the string using a tape measure. Round the measurement to the nearest 1/16 inch. Record your measurement as "V-belt length."

Measure the width of the span between both sides of one of the engine pulleys. The span across the "V" in the pulleys represents the width of the belt. Round the measurement to the nearest 1/16 inch. Record your measurement as "pulley width."

Combine the two measurements you have made for the V-belt to determine the V-belt size you will need for your engine.


Some belt manufacturing companies offer online applications for sizing a belt (see References section).

Things You'll Need

  • Spool of string
  • Tape measure
  • Scissors
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About the Author

Tim Petruccio is a professional writer and automotive mechanic. His writing combines more than 20 years of mechanical experience in automotive service, service management, automotive education and business ownership. He assisted in the automotive beta, which launched March 2011.