Bow String Length Calculator

Precision Bowstring Measurement for Traditional & Compound Bows

Recommended Actual String Length:

AMO Reference: 62.00″

Calculation Method: AMO Standard (-4″)

Suggested Twists: 15-25 (depending on material)

Standard Bow String Length Calculator Reference Table

Bow Length (AMO)	Recurve String Length (-4″)	Longbow String Length (-3″)
58″	54″	55″
60″	56″	57″
62″	58″	59″
64″	60″	61″
66″	62″	63″
68″	64″	65″
70″	66″	67″

What is a Bow String Length Calculator?

A bow string length calculator is an essential tool for archers, bowyers, and technicians who need to determine the precise physical length of a replacement string. Whether you are using a modern recurve, a traditional longbow, or a high-performance compound bow, the bow string length calculator ensures that your equipment operates within its designed mechanical specs. Many beginners mistakenly assume that a 62-inch bow requires a 62-inch string; however, in reality, the string must be shorter to create the necessary tension (brace height) required to propel an arrow efficiently.

Who should use a bow string length calculator? Competitive target archers, hunters, and hobbyists all benefit. Using an incorrectly sized string can lead to poor accuracy, excessive noise, or even physical damage to the bow limbs. By inputting the AMO (Archery Manufacturers Organization) length, the bow string length calculator provides an “actual length” measurement that accounts for the necessary reduction based on bow type.

Bow String Length Calculator Formula and Mathematical Explanation

The math behind a bow string length calculator relies on industry standards established decades ago to simplify the process of ordering strings. The calculation depends primarily on the geometry of the bow limbs and the desired brace height.

The AMO Standard Formula:

• Recurve Bows: Actual String Length = AMO Length – 4 inches
• Longbows: Actual String Length = AMO Length – 3 inches
• Compound Bows: These typically use specific manufacturer measurements, but a bow string length calculator can estimate based on Axle-to-Axle (ATA) dimensions.

Variables used in the bow string length calculator

Variable	Meaning	Unit	Typical Range
AMO Length	Standardized bow length measurement	Inches (“)	48″ – 72″
Brace Height	Distance from grip to string	Inches (“)	7″ – 9.5″
Twist Rate	Number of rotations in the string	Total Twists	10 – 30

Practical Examples (Real-World Use Cases)

Example 1: The Modern Recurve Archer
An archer has a bow marked “AMO 66”. Using the bow string length calculator, they select “Recurve” and enter 66. The calculator applies the -4″ rule, resulting in a recommended actual string length of 62 inches. This length allows the archer to achieve a standard 8.5-inch brace height after adding approximately 20 twists to the string.

Example 2: The Traditional Longbow Hunter
A hunter uses a custom 64″ longbow. They need a new Flemish twist string. By entering 64 into the bow string length calculator under the “Longbow” setting, the tool subtracts 3 inches. The resulting 61-inch string ensures the longbow maintains its classic profile and provides enough limb preload for a quiet shot.

How to Use This Bow String Length Calculator

Using the bow string length calculator is straightforward and designed to prevent ordering errors:

1. Select Bow Type: Choose between Recurve, Longbow, or Compound. This sets the internal mathematical constant (3″ vs 4″).
2. Enter AMO Length: Look at the lower limb of your bow. It will usually have a label like “AMO 62” or “62\””. Enter this number.
3. Adjust Brace Height: Enter your preferred brace height. While this doesn’t change the base string length, it helps you understand how many twists you might need.
4. Read the Result: The large green box displays the “Actual String Length.” This is the number you provide to string makers.
5. Copy and Save: Use the copy button to save your specs for your next purchase.

Key Factors That Affect Bow String Length Results

Several technical factors can influence the final output of the bow string length calculator and how the string performs in the field:

• Material Creep: Modern materials like BCY 452X stretch less than Dacron (B55). If using Dacron, you might need a slightly shorter string initially.
• Twist Density: Adding twists to a string effectively shortens it. A bow string length calculator assumes a standard twist rate.
• Limb Geometry: Highly aggressive recurve limbs may occasionally require a -4.5″ reduction instead of -4″.
• String Type: Endless loop strings have fixed lengths, whereas Flemish twist strings can be slightly adjusted during the braiding process.
• Temperature: Extreme heat can cause some synthetic fibers to expand, slightly altering the effective length.
• Manufacturer Variations: Not all manufacturers follow the AMO standard perfectly; always check the manual if the bow string length calculator results seem significantly different from your current setup.

Frequently Asked Questions (FAQ)

1. Why is the string length shorter than the bow length?

The bow needs to be “pre-loaded” or bent to create tension. If the string were the same length as the bow, it would hang limp and could not store energy.

2. Can I use a recurve string on a longbow?

Generally no. As shown by the bow string length calculator, recurves require a 4″ reduction while longbows require 3″. Using a recurve string on a longbow would likely result in an dangerously high brace height.

3. What if my bow isn’t marked with an AMO length?

Measure the bow from tip to tip along the belly (the side facing the shooter) following the curves. This provides a rough estimate for the bow string length calculator.

4. How many twists should a bowstring have?

Most strings perform best with 0.5 to 0.75 twists per inch of length. This helps the string stay round and consistent.

5. Does the number of strands affect the length?

No, the number of strands affects the thickness and weight, but the bow string length calculator focuses purely on the longitudinal measurement.

6. Is AMO the same as tip-to-tip length?

In the AMO standard, the bow length is the string length plus 3 or 4 inches, which roughly corresponds to the length of the bow when unstrung, measured along its back.

7. What happens if my string is too long?

If the bow string length calculator output is ignored and a string is too long, your brace height will be too low, leading to wrist slap and poor arrow flight.

8. Are compound bow strings calculated differently?

Yes, compound bows use a system of cables and strings. While a bow string length calculator can provide estimates, it’s always best to use the manufacturer’s spec sheet for compounds.