How to Measure Compound Bow String Length

Did you know that original bow strings were made from animal parts, like sheep or goat intestines? Other ancient materials used were fiber, flax, linen, or hemp strings.

We’ve come a long way from those days thousands of years ago. When you select your own bow string lengths, you are participating in the sport of archery, which has an incredibly long and rich history.

As any master archer can tell you, that, besides the bow itself with its limbs and risers and arrow rest, the bow string is the most important component of the entire tool.

Compound Bow Cables and Strings

Unlike regular bows or long bows, which have bent limbs, compound bows have stiff limbs. When you hold the two models up side by side, you can definitely see the difference.

With their cams, axles, pulleys, cables, and strings, compound bows are much more complex than regular bows. They were designed to give you, as the archer, a distinct mechanical advantage over older bow models. The compound bow gives you so much more force, which in turn, makes the arrow shoot forward with far more momentum. Compound bows are often used for hunting precisely because of their advanced design.

However, so many cables and strings can prove to be confusing. They attach in different places on the bow, and each one serves a different purpose. They also stretch too much and have to be replaced. You could even have one break.

Bow strings are different from the two other cables found on a compound bow: the bus cable and the control cable. The bus cable is connected to the axles, and the control cable (or cables) are attached to the cams. Control cables have serving ends. Cables are also attached to cable slides, while the actual bow string is not.

Why is having the proper bow string length so important? It has to do with one crucial factor: draw weight.

Bow String Creates Draw Length

Draw length is the measurement of how many inches are between the arrow rest on the compound bow and the maximum arm span when you pull the arrow back. You don’t want the bow string to be too long, for then you would lose tension and not be able to create the force necessary to shoot the arrow. But, neither do you want it to be too tight, for then it’s too difficult to pull the arrow back. So, it’s very important to determine the correct bow string length for your bow.

How Long Should the Bow String Be?

Many compound bow owners leave the string length up to the bow’s manufacturer or an expert at a sporting goods store to measure it for them. But, it is highly useful to know your particular bow’s requirements. Your bow probably already came with strings, so you can simply use that exact string length. Use a tape measure and hold it end to end.

But if your bow did not come with strings, then here are some simple tips and tricks you can use to determine the proper bow string length.
There are two proper methods you can use: either manually measuring or going by the AMO (Archery Manufacturers and Merchants Organization) length. We’ll discuss both below.

First Method: Manually Measuring Your Compound Bow

It’s easy to measure the bow string length required for a long bow or recurve bow. On a compound bow, it’s a little bit more involved. You will need some equipment:

• A bow press
• A long piece of regular white string or twine
• A permanent marker
• A tape measure

You are going to measure from one outside pin on the cam at the end of the top riser to the other outside pin on the other cam at the end of the bottom riser.

Step 1

Once you have the proper equipment, then place the compound bow in a bow press, with the risers facing towards you. If you don’t have a bow press, a partner can help you compress the bow. You can’t string a bow and compress it at the same time, so you’ll need a partner. Tighten the bow press vise grip, making the bow upside down and facing towards you. The cable slide should be in the middle and vertical.

Step 2

Make a loop on one end of the long piece of string or twine. Tie a good knot so that it holds firmly.

Step 3

Place this loop over the pin on the cam on the top riser, which is facing you on your right-hand side. Wind it around the cams like you would a regular bow string.

Step 4

Pull the string towards the other cam, compressing the bow at the same time. Gently insert it into the other cam on your right-hand side and wind it.

Step 5

Mark the string at the end using a permanent marker the length that you are going to purchase. Unwind the string from the cam and then unwind it from the other cam.

Step 6

Use a tape measure to measure the length of the string from the loop to the point where you marked it.

Second Method: Using the AMO Length

If you’re lucky enough to have a compound bow that’s clearly marked with the standardized AMO length, you can use that to determine the bow string. A label might include the weight, string length, cable, and draw. For a compound bow weighting between 50 and 65 pounds, the string length would be 58”. It’s a lot easier than manually measuring.

Conclusion

Besides searching for your bow string length on the internet, you can also call the manufacturer of your bow, give them the overall length, and ask them what string size that you need. However, it is handy to know how to measure string length, if only because you might want to restring them yourself. A bow press is an excellent investment of your time and money, and it will make that job a lot easier.