Bow String Length Calculator

Instantly determine the correct string length for your traditional bow with our easy-to-use bow string length calculator. Get precise results based on AMO standards for recurve and longbows.

Calculate Your String Length

Common Lengths for Your Bow Type

AMO Bow Length	Estimated String Length

Example string lengths based on the selected bow type (Recurve). This table updates when you change the bow type.

What is a Bow String Length Calculator?

A bow string length calculator is a specialized tool designed to estimate the correct actual length of a bow string needed for a traditional bow, such as a recurve or longbow. Bows are typically marked with an “AMO Length,” which is a standard set by the Archery Manufacturers and Merchants Organization (now the Archery Trade Association, ATA). However, the AMO length is NOT the actual length of the string you need to buy. The actual string is always shorter to allow the bow to be braced correctly, creating the necessary tension in the limbs. This bow string length calculator bridges that gap by applying a standard rule of thumb.

Anyone who owns or shoots a traditional recurve or longbow should use a bow string length calculator. It is especially useful for beginners who are buying their first replacement string, or for archers who have acquired a used bow without a string. A common misconception is that a 68-inch bow needs a 68-inch string. This is incorrect and will result in a string that is far too long, making it impossible to brace the bow. Using our precise bow string length calculator ensures you get a usable length from the start.

Bow String Length Formula and Mathematical Explanation

The calculation performed by this bow string length calculator is based on a widely accepted industry guideline for traditional bows. The formula is straightforward:

Actual String Length = AMO Bow Length - Deduction

The “Deduction” value depends on the type of bow:

• For Recurve Bows: The standard deduction is 4 inches.
• For Longbows: The standard deduction is 3 inches.

This difference exists because the geometry of a recurve bow’s limbs requires a slightly shorter string to achieve the proper brace height compared to a longbow of the same AMO length. Our bow string length calculator automatically applies the correct deduction based on your selection.

Variables in the Bow String Length Calculation

Variable	Meaning	Unit	Typical Range
AMO Bow Length	The standardized length of the bow, as marked by the manufacturer.	Inches	48″ – 72″
Deduction	The amount subtracted from the AMO length to find the actual string length.	Inches	3″ or 4″
Actual String Length	The estimated physical length of the string needed, measured end-to-end.	Inches	45″ – 69″

Practical Examples (Real-World Use Cases)

Example 1: Standard Recurve Bow

An archer has a popular 62″ AMO recurve takedown bow. They need to order a new string. Using the bow string length calculator:

• Input – Bow Type: Recurve
• Input – AMO Bow Length: 62 inches
• Calculation: 62″ – 4″ = 58″
• Output – Estimated String Length: 58 inches. The archer should look for a string that has an actual physical length of 58 inches.

Example 2: Traditional Longbow

A traditional archer owns a 70″ AMO English longbow and wants to get a spare string. They use the bow string length calculator to determine the size.

• Input – Bow Type: Longbow
• Input – AMO Bow Length: 70 inches
• Calculation: 70″ – 3″ = 67″
• Output – Estimated String Length: 67 inches. They should order a 67″ string. Knowing this is crucial, and our bow string length calculator provides this clarity instantly.

How to Use This Bow String Length Calculator

Using this calculator is simple and efficient. Follow these steps to get your result:

1. Select Bow Type: First, choose whether you have a “Recurve Bow” or a “Longbow” from the dropdown menu. This is the most critical step as it determines the deduction value.
2. Enter AMO Bow Length: Input the AMO length of your bow in inches. This number is almost always written on the bow’s lower limb, often near the draw weight information.
3. Read the Results: The calculator instantly updates. The primary result is the “Estimated String Length” you need. You can also see the intermediate values, including the deduction that was applied.
4. Decision-Making: When purchasing a new string, look for one that specifies its “actual length” as the value provided by this bow string length calculator. If a string is sold by “AMO length,” a “68-inch AMO string” should, in theory, have an actual length of 64-65 inches. Our calculator helps you know what that actual length should be. For more on this, check out our guide on AMO bow length vs string length.

Key Factors That Affect Bow String Length Results

While this bow string length calculator provides an excellent starting point based on industry standards, several factors can influence the *perfect* string length for your specific setup. Fine-tuning may be required.

1. String Material: Modern synthetic materials like Dyneema (Fast Flight, BCY 8125) stretch very little compared to older materials like Dacron (B-50). If you order a Dacron string, it may stretch slightly over time, so starting with a slightly shorter string (e.g., an extra 1/4″ to 1/2″ shorter) might be necessary.
2. Brace Height Preference: Brace height is the distance from the deepest part of the grip to the bowstring when strung. A slightly shorter string increases brace height, while a longer string decreases it. Some archers prefer a higher or lower brace height for tuning purposes, which might lead them to choose a string that’s +/- a half-inch from the calculated result.
3. Number of Twists: A Flemish twist or endless loop string can be twisted to shorten its length slightly. A good string should allow you to achieve the desired brace height with a reasonable number of twists (e.g., 15-30). The result from our bow string length calculator assumes a standard number of twists will be applied.
4. Manufacturer Variations: While AMO is a standard, not all bowyers follow it with perfect precision. Some custom or older bows might have unique geometries that require a string length different from the standard -3″ or -4″ rule.
5. Loop Size: The size of the loops on the end of the bowstring can affect its overall functional length. Larger loops can make the string act slightly longer. This is a subtle factor but relevant for expert archers seeking perfect tuning.
6. Physical Wear and Tear: Over time, a bowstring can stretch and creep, especially under heavy use or if made from materials like Dacron. An old, stretched-out string might be longer than when it was new. Always use a reliable tool like our bow string length calculator for a fresh baseline. Find out more about how to measure bow string length correctly.

Frequently Asked Questions (FAQ)

1. What does AMO stand for?

AMO stands for the Archery Manufacturers and Merchants Organization. It created standards for consistency in archery equipment, including bow length. The organization is now known as the Archery Trade Association (ATA), but the “AMO standard” designation is still widely used.

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

Sometimes, but it’s not ideal. The main difference is often the size of the top loop; recurve strings typically have larger loops to fit over the curved limb tips. A recurve string might fit on a longbow, but a longbow string’s smaller loop will likely not fit on a recurve. More importantly, using a string that is 4″ shorter (recurve standard) on a longbow that needs a 3″ shorter string will result in an excessively high brace height. It’s best to use the correct type as determined by a bow string length calculator. A recurve bow string length is different for a reason.

3. What happens if my string is too long or too short?

If the string is too long, you won’t be able to achieve the recommended brace height, or you may not be able to brace the bow at all. This leads to poor arrow flight and a loud, inefficient shot. If the string is too short, the brace height will be too high, which can put excessive strain on the limbs and may also lead to poor performance. Our bow string length calculator helps avoid both extremes.

4. Does this calculator work for compound bows?

No. Compound bows have a highly specific string and cable system. You MUST use the exact length and material specified by the manufacturer. Do not use this bow string length calculator for any compound bow.

5. How do I find my bow’s AMO length if it’s not marked?

You can measure it yourself. Unstring the bow. Run a flexible measuring tape along the belly of the bow (the side facing you when you shoot), following the curve of the limbs from one string groove to the other. This measurement is your approximate AMO length.

6. Why is a longbow string deduction only 3 inches?

Longbows have relatively straight limbs compared to the significant curves of a recurve. Because of this simpler geometry, the string does not have to travel as far “forward” to brace the bow, so it can be slightly longer relative to the bow’s total length. Consult a longbow string length chart for common sizes.

7. Is the result from the bow string length calculator always perfect?

It’s a very accurate starting point based on a universal standard. However, due to factors like string material and specific bowyer designs, you may need to make minor adjustments by twisting the string or trying a length that is a half-inch different. Think of this calculator as getting you 99% of the way there.

8. What is brace height and how does it relate to string length?

Brace height is the distance from the deepest part of the grip to the string when the bow is strung. String length directly controls brace height. A shorter string pulls the limbs back further, increasing brace height. A longer string is looser, decreasing it. Finding the right brace height is a key part of tuning your bow, and it all starts with having the right length string from a tool like this bow string length calculator.