How to measure fan belt size

The fan belt is an important accessory in your automobile. It may be a bit tricky to measure because it rarely connects only to a fan. It goes around a pulley in your engine that attaches to a flywheel. It often powers motors or pumps to the power steering, air conditioner compressor, alternator, power brakes or the water pump. If your fan belt is frayed or has nicks or torn areas, it is time to replace it. Measuring your fan belt is not difficult to accomplish if you are able to follow its pathway.

Look for a diagram underneath your bonnet that shows the path of your fan belt. Normally, it is located on the plastic cover over the cooling fan.

Cut a long length of thin rope, approximately three to five feet in length.

Place it on one portion of the fan belt.

Hold it in place with the thumb and forefinger of your non-dominant hand.

Follow the path of the fan belt with the rope. Make sure you follow the exact path and that there is no slacking of the rope along the pathway.

Mark the spot on the rope with a permanent marker where it meets the place you are holding with the other hand. Try to get the measurement as exact as you possibly can by gripping the rope firmly against the fan belt.

Remove the rope and measure it with a tape measure. Write down the measurement.

Use the tape measure to determine the thickness of the fan belt by measuring its cross-section.

Shop for a new fan belt at an auto parts supply or a discount store. If the new fan belt is a millimetre or so too short, it will probably work just fine, as it will loosen over time.


Try to find the old belt number on the exposed surface of the fan belt. This is an effective way to ensure you purchase the correct size. The numbers may be worn off if it is old or unusually frayed.


Do not purchase a fan belt that is too long because it will not work properly.

Things You'll Need

  • Thin rope
  • Tape measure
  • Pen and paper
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About the Author

Chelsea Fitzgerald covers topics related to family, health, green living and travel. Before her writing career, she worked in the medical field for 21 years. Fitzgerald studied education at the University of Arkansas and University of Memphis.