How to Measure a Rubber Belt

It is very important that you read and follow these instructions exactly and completely.   Belts are not exchangable, refundable, or returnable.    If you order the wrong size belt because you measured incorrectly, you cannot return them.   If you have any questions about the measuring process, please ASK US before you place your order.

How are belts measured?
The numerical portion of belt part numbers represent the total circumference in inches (as if the the belt was cut and laid out flat on a ruler, without being stretched beyond its relaxed length.) 

Broken belt
If your belt is broken at one spot, it is very easy to measure - just lay it alongside a ruler and measure its length in inches.  Deduct 5%-10% to compensate for stretching of the old belt.   Keep reading below:

Complete unbroken belt, but stretched
If the belt is complete (unbroken), you measure the length of the complete belt along a ruler (in inches) and then double that measurement (deduct 5%-10% to compensate for stretching).   Keep reading below:

Missing belt, or old belt turned to goo
If the belt has turned to goo and is unmeasurable, measure the belt path in inches with a string pulled very taut (wrap the string around the pulleys just as the belt would go) .    Cut through the string at the point where it overlaps, discard the ends and then measure the length of the string (in inches) that was wrapped around the pulleys.   This is the actual length of the belt path.   Deduct 5% to 10% to compensate for stretching.   Order a belt with the resulting length (in inches).   Cassette decks normally need either the FBS series (flat belt about about 1/8" wide) or the SBS series (thin square belt).    CD players and DVD players normally use the SBM size belt.    VCRs use the SBL size belt in most cases, and if it is a flat belt, the FBM size.

First, read the rest of the instructions below.   Still have questions?  Ask us here before you order.   Remember, incorrect belt sizes are not returnable, refundable, or exchangable.

Specific Instructions for Complete Belts (not broken):

#1 - Get a ruler, 2 pens, and the old belt.


#2 - Pull belt just snug and measure length in inches (don't stretch!)

Now, double the length that you just measured!  This is very, very important!


(If you haven't read the above step about multiplying the length you measured by 2, now would be a good time!)

(Note - broken belts, or belt path measurements with a string, are NOT to be doubled.)


:  Measure and choose your belts carefully.   Belts are NOT returnable.

If you have any questions about the measuring process, please ASK US before you place your order.


Belt above would have an approx 9 inch inside circumference (4.5" x 2).

   The next step is to deduct 5% to 10% for stretching!

If you assume 5% stretching, the belt above in the example would be 9.0 - 0.45 ~ 8.6" IC
If you assume 10% stretching, 9.0 - 0.90 = 8.1" IC
In this case you would choose a replacement belt between about 8.0 and 8.7 inches

#3 - Measure belt thickness in inches.
Above belt is a little over 1/16" thick or around .065"

More on determining the thickness of square belts:

Our SBX series of belts (.090") are just a bit thicker than a U.S. Half Dollar (.085")
Our SBL series of belts (.075"-.079") are the thickness of a U.S. Nickel (.077")
Our SBM series of belts (.065") are the thickness of a U.S. Quarter (.066")
Our SBS series of belts (.046") are just a bit thinner than the thickness of a U.S. Dime (.051")
Our SBO series of belts (.039") are just a bit thicker than the thickness of a credit card (.033")

So, above belt would be about .065" thick, and between 8.0 and 8.7 inches.  If your exact size isn't in our database, pick a belt which is reasonably close.  From our database, you'll see that we have a three belts which could work for our example above:




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Calculator for your use in determining belt size: