Bow String Length Calculator
Quickly estimate the recommended actual string length for traditional bows using AMO bow length standards. Enter your bow length, choose the bow style, and get a clean starting point for string length, brace height range, and setup guidance.
Calculate Your Recommended String Length
Expert Guide to Using a Bow String Length Calculator
A bow string length calculator helps archers estimate the right starting string size before they buy, build, or replace a string. For traditional bows, especially recurves and longbows, the process is much simpler than it is for compound equipment. If you know the AMO bow length, you can usually determine the actual string length with a reliable rule of thumb: the string is commonly about 3 inches shorter than the bow’s AMO length. That simple relationship is why a dedicated bow string length calculator is so useful. It takes a standard measurement system and turns it into a practical answer you can use in seconds.
Still, even though the math is easy, selecting the correct string is not just about one number. The bow style, the target brace height, the material used, and the way the string is twisted after installation all influence the final setup. This guide explains the sizing logic, shows practical examples, and outlines what to check before ordering your next string.
What bow string length actually means
Many archers confuse bow length with string length, but they are not the same measurement. Bow length is usually stated as AMO length, a common industry reference size used for traditional bows. String length, by contrast, is the actual physical length of the string in its proper measuring condition. If your recurve is labeled as a 68-inch bow, that does not mean you buy a 68-inch string. In common traditional sizing, you start with a string that measures about 65 inches actual length.
This is where a calculator becomes valuable. It removes guesswork and gives you a consistent baseline. You can then fine-tune brace height by adding or removing twists in the string. For many bowyers, pro shops, and traditional archers, this two-step process is standard: first get the correct nominal size, then tune the final setup.
Key terms to know
- AMO bow length: The reference bow length commonly used for recurves and longbows.
- Actual string length: The measured length of the string itself, which is shorter than the AMO bow length.
- Brace height: The distance from the deepest part of the grip pivot point to the bowstring when the bow is strung.
- Twists: Rotations added to the string to shorten it slightly and increase brace height.
- String material: Fibers such as Dacron or modern low-stretch materials that affect break-in behavior and feel.
The standard formula behind the calculator
For most traditional recurve and longbow applications, the standard starting estimate is:
Actual string length = AMO bow length – 3 inches
That is the core calculation used in this page’s bow string length calculator. If your bow length is entered in centimeters, the calculator converts it to inches, applies the formula, and then converts the output back to your selected unit for convenience.
The tool also estimates a typical brace height range. This matters because two strings that are nominally the same can settle differently after installation. A string that is theoretically correct may still need twists to reach the sweet spot for noise, arrow flight, and limb feel. In practice, a calculator gives you the right size to order, while brace height tuning gives you the right performance.
Common sizing examples
| AMO Bow Length | Estimated Actual String Length | Typical Use Case |
|---|---|---|
| 58 in | 55 in | Short hunting recurve |
| 60 in | 57 in | Compact traditional bow |
| 62 in | 59 in | Versatile field recurve |
| 64 in | 61 in | Traditional target and hunting crossover |
| 66 in | 63 in | Common recurve length for adults |
| 68 in | 65 in | Popular target recurve standard |
| 70 in | 67 in | Longer draw archers and smooth target setup |
Why brace height matters after you calculate string length
Even a perfectly sized string is only the beginning of tuning. Brace height affects arrow clearance, bow noise, vibration, and how the bow feels in the hand. A bow set too low can feel loud and harsh. A bow set too high may lose some cast and feel less forgiving if you move too far outside the maker’s recommended range.
That is why serious archers use a bow string length calculator and then immediately confirm the resulting brace height. Think of the calculator as the sizing stage and brace height tuning as the refinement stage.
Typical starting brace height ranges
| AMO Bow Length | Typical Recurve Brace Height | Typical Longbow Brace Height |
|---|---|---|
| 58 in | 7.5 to 8.25 in | 6.5 to 7.25 in |
| 62 in | 8.0 to 8.75 in | 6.9 to 7.65 in |
| 66 in | 8.5 to 9.25 in | 7.3 to 8.05 in |
| 68 in | 8.75 to 9.5 in | 7.5 to 8.25 in |
| 70 in | 9.0 to 9.75 in | 7.7 to 8.45 in |
These values are practical reference bands rather than hard rules. Always compare them against the bowyer’s recommendation, especially for custom longbows, reflex-deflex designs, or performance limbs.
How to measure your bow correctly before using the calculator
- Confirm the bow type. This calculator is intended for traditional recurve and longbow sizing.
- Use the AMO bow length. If the manufacturer lists the bow as 68 inches AMO, enter 68. If your measurement is in centimeters, convert or let the calculator do it.
- Check whether the current string was custom built. An older custom string may not match the labeled size on the bow exactly.
- Review manufacturer notes. Some bow makers specify a preferred brace height range or a custom string length that differs from the generic standard.
- Tune after installation. Once the string is installed, use twists to dial in brace height and verify quiet shooting.
Common mistakes to avoid
- Ordering a string equal to the bow’s labeled AMO length.
- Using compound bow assumptions for a recurve or longbow.
- Ignoring break-in stretch with Dacron strings.
- Skipping brace height measurement after replacing the string.
- Assuming every 68-inch bow shoots best at the exact same brace height.
String material and its effect on real-world setup
String material does not usually change the initial nominal length formula, but it does change how the bow behaves during the first several shooting sessions. Dacron, often associated with B-50 style strings, is more forgiving and traditionally preferred for older bows or limbs that are not rated for high-performance low-stretch material. However, Dacron tends to settle more. That means your brace height can drop slightly after the first break-in period, which may require re-twisting the string.
Modern low-stretch materials typically hold their tune better, give a crisp shot cycle, and can maintain brace height more consistently over time. Flemish twist strings, meanwhile, are popular for traditional aesthetics and can tune beautifully, though the build style and serving thickness still affect how the final setup feels.
Practical takeaway: Use the calculator to get your starting string length, then verify brace height after installation and again after the first 30 to 100 shots. That habit prevents most sizing and noise complaints.
How accurate is a bow string length calculator?
For standard traditional bows, a good calculator is highly accurate as a starting estimator. In most cases, the result gets you to the correct string size for ordering or building. The remaining variation happens during tuning, not during basic sizing. That is why archers who understand AMO sizing often order with confidence from a simple formula.
Where calculators become less exact is with custom builds, unusual limb geometry, heavily recurved tips, and bows made outside common sizing conventions. In those cases, the best practice is to ask the bowyer for the intended string length or recommended brace height range, then use the calculator only as a sanity check.
When you should not rely on a generic calculator alone
- Compound bows with manufacturer-specific string and cable lengths
- Vintage bows with unclear labeling
- Homemade bows without standardized AMO references
- Custom longbows where the bowyer provided a dedicated string spec
Archery references and educational resources
If you want to deepen your understanding of archery equipment, setup, and safety, these educational resources are useful starting points:
- Penn State Extension 4-H Shooting Sports
- University of Nebraska-Lincoln 4-H Shooting Sports
- University of Maryland Extension Shooting Sports
These sources are not product catalogs. They are educational programs that support safe, informed participation in archery and shooting sports, making them strong authority references for beginners and experienced archers alike.
Final advice for choosing the right bow string length
The best way to use a bow string length calculator is to think in stages. First, enter the correct AMO bow length and get the actual string length estimate. Second, install the string and measure brace height. Third, tune with twists until the bow shoots quietly and consistently within the recommended range. This process is simple, repeatable, and effective for the majority of recurve and longbow shooters.
If you are buying a replacement string online, the calculator can save time and prevent one of the most common errors in archery equipment ordering: choosing a string equal to the labeled bow length. If you are building your own strings, the calculator gives you a clear baseline before you make final adjustments for serving thickness, loop size, and material behavior.
In short, the calculator gives you the right starting point. Your brace height gauge, your ears, and your arrow flight finish the job. Use all three together and you will get a better shooting bow, a more repeatable setup, and far less frustration when replacing strings in the future.