Enter the bow’s AMO/marked length and select a bow type (recurve/longbow) in the Bow String Length Calculator. Then enter either bow length or string length, and the calculator will estimate the missing value using common AMO/ATA string-sizing guidelines.

Bow String Length Calculator

Select a bow type, then enter exactly 1 of the two length values to calculate the other.

Related Calculators

Bow String Length Formula

The following two example problems outline the steps and information needed to calculate the Bow String Length using common AMO/ATA guidelines for traditional bows. (Compound bows do not use this simple rule; use the manufacturer’s specified string length.)

BSL = BL - k
  • Where BSL is the Bow String Length (in)
  • BL is the bow’s AMO/marked bow length (in)
  • k is the typical AMO/ATA deduction: about 3 in for many recurves and about 4 in for many longbows (check the bow manufacturer’s recommendation)

To estimate a bow string length under AMO/ATA guidelines, subtract k inches from the bow’s AMO/marked length (commonly 3 in for many recurves or 4 in for many longbows).

How to Calculate Bow String Length?

The following example problems outline how to calculate Bow String Length.

Example Problem #1:

  1. First, determine the bow’s AMO/marked length (in) and the bow type.
    • The bow length (in) is given as: 30.
    • Assume a longbow guideline (k = 4 in).
  2. Finally, calculate the Bow String Length using the equation above: 

BSL = BL – k

The values provided above are inserted into the equation below and computed.

BSL = 30 – 4 = 26 (in)

Example Problem #2: 

For this problem, the variables required are provided below:

bow length (AMO/marked length) (in) = 40

Test your knowledge using the equation (choose an appropriate k for your bow type) and check your answer with the calculator.

BSL = BL – k = ?