Complete Guide to Bow String Length Calculator Results, AMO Standards, and String Sizing
What is bow string length?
Bow string length is the actual physical length of the string used on your bow. In modern archery, that number is often related to AMO bow length rather than measured directly by laying a string flat and reading it with a tape. If you are shopping for a replacement, you normally start with your bow’s AMO length and then apply a known offset for your bow style. A bow string length calculator helps you do that quickly and consistently.
Correct string length matters because it affects brace height, shooting feel, tune, and even how safe your setup feels during draw and release. A string that is too long can produce a low brace height and sluggish behavior. A string that is too short can push brace height too high and alter limb geometry. The right size creates a predictable baseline before fine tuning with twists.
How this bow string length calculator works
This calculator uses a simple sizing logic that many archers follow for recurve and longbow setups: estimated string length equals AMO bow length minus an offset. The offset defaults by bow type. For many recurves and longbows, a 3-inch subtraction is common. Traditional bows sometimes use a larger offset, often around 3.5 inches. Because bows vary by maker, profile, and limb design, this result is best treated as a high-quality estimate for ordering and setup.
The tool also converts between inches and centimeters, rounds to the nearest 1/8 inch for practical ordering, and can suggest twist direction when you enter current and target brace height. If target brace height is higher than current, the string generally needs shortening via added twists. If target brace height is lower, untwisting may help, within safe limits.
AMO standard explained
AMO (Archery Manufacturers and Merchants Organization) sizing language was developed to simplify compatibility across brands. When archers discuss a “68-inch recurve,” they are often speaking in AMO terms. Replacement strings are then chosen using a corresponding AMO-to-string relationship. This framework makes ordering easier than relying on improvised measurements that can change based on tension and handling.
A critical detail: AMO notation is a standard reference, not a guarantee that every bow from every brand uses exactly the same practical offset in all conditions. Limb shape, riser geometry, and intended brace-height window can shift what feels ideal. That is why many experienced archers calculate a baseline size and then tune with controlled twists and chronograph/impact feedback.
How to measure a bow for correct string length
If your bow documentation is available, always begin with the published AMO bow length and the manufacturer’s recommended string length. If documentation is not available, measure carefully and work from known standards. Use a rigid tape, verify that your bow model identification is correct, and avoid measuring old worn strings as your only reference because creep and serving movement can distort the number.
For recurve and longbow users, a practical method is:
- Find the bow AMO length from model specifications.
- Apply a typical offset (often 3 inches for recurve/longbow, sometimes 3.5 for traditional setups).
- Install and tune to target brace height using twists.
- Record final twist count and brace height for future replacements.
For compound bows, sizing is different. Compound systems use exact string and cable lengths specific to cam geometry, axle-to-axle setup, and timing requirements. If you shoot compound, rely on official manufacturer charts or a pro shop spec sheet rather than generalized offsets.
Brace height, twisting, and tuning
Brace height is one of the first tuning checkpoints after installing a new string. It is the distance from the string to the deepest part of the grip (pivot point) when the bow is at rest. Small changes in brace height can influence noise, forgiveness, arrow flight feel, and how stable the bow seems through release.
Twisting the string shortens effective length and raises brace height. Untwisting lengthens effective string and lowers brace height. This calculator provides a practical estimate for twist direction based on your current and target numbers. Use it as guidance, then verify on your bow with a proper bow square and repeated measurement.
Good practice is to make adjustments in small steps, check nocking point and tiller interaction as needed, and shoot enough arrows at each setting before concluding that a brace height is better or worse. Noise reduction and clean paper tears can both be useful indicators, but overall consistency at your normal distance should remain the final judge.
String materials and stretch behavior
String material influences how your setup settles after installation. Dacron-style materials generally stretch more and are often preferred for some older bows that are not rated for low-stretch high-performance fibers. Modern high-modulus materials can hold tune more aggressively and deliver crisp response, but they may require precise construction and compatible limb tips.
Because material affects settling behavior, two strings with the same nominal length can feel different after break-in. That is normal. Always account for strand count, center serving diameter, and end-loop fit. A perfect length with poor serving compatibility can still produce inconsistent nock fit and erratic launch behavior.
Common bow string sizing mistakes
The most frequent mistakes include ordering solely by old string measurement, ignoring AMO references, using the wrong unit conversion, and overlooking brace-height windows published by the bow maker. Another common issue is assuming compound bows can be treated like recurves in sizing. They cannot; cable and cam systems demand exact lengths and timing.
Avoiding these mistakes is straightforward: start from specs, calculate carefully, verify units, install safely, and tune incrementally. Keep notes after final tuning so your next replacement is simple and repeatable.
FAQ: Bow String Length Calculator and String Sizing
What is the basic recurve bow string formula?
A common baseline is string length = AMO bow length − 3 inches. Then fine tune with twists to reach your preferred brace height.
Can I use this calculator for longbow string length?
Yes. Longbows frequently follow similar AMO offset logic, though exact values can vary by design and maker.
How accurate is a bow string length calculator?
It is very useful for initial sizing, especially when paired with known AMO standards. Final performance still depends on material, build quality, and tuning.
Should I measure my old string to buy a new one?
Use old-string measurement only as a reference. Manufacturer specs and AMO sizing are usually more reliable.
Do compound bows use the same AMO minus offset method?
No. Compound bows require exact model-specific string and cable lengths from manufacturer data.
If you want a fast and reliable replacement workflow, use this bow string length calculator for an initial estimate, then confirm with your bow manufacturer’s recommendations whenever possible. That approach gives you speed, consistency, and better tuning outcomes from day one.