Bowstring Length Calculator

Example string length calculation

Let's calculate string length for a typical recurve bow:

For a 68" AMO recurve, a 64" AMO string is standard. The actual string will measure slightly longer due to loops and serving, but is ordered as "64 inches AMO."

Understanding bowstring length

What is AMO length?

AMO (Archery Manufacturers Organization) standardized how bow and string lengths are measured. For recurve and longbows, AMO length refers to the bow length, not the string length. This prevents confusion across manufacturers.

The rule: String length is typically 3-4 inches shorter than bow AMO length.

• 62" AMO bow → 58-59" string
• 66" AMO bow → 62-63" string
• 68" AMO bow → 64-65" string
• 70" AMO bow → 66-67" string

The exact difference depends on desired brace height (distance from grip to string at rest). Higher brace height = slightly shorter string. Lower brace height = slightly longer string.

Measuring existing strings

Recurve/Longbow strings:

1. Remove string from bow (never measure under tension)
2. Lay string flat on floor or table
3. Measure from the INSIDE of one loop to the INSIDE of the other loop
4. This is your AMO string length
5. The physical string will be 1-2 inches longer due to loop size

Compound bow strings:

1. Remove string from bow (or measure very carefully if installed)
2. Measure from where serving ends on one side to where serving ends on other side
3. Do NOT include the loops or end servings in measurement
4. Measure string relaxed, not stretched
5. This is your actual string length - order this exact length

Why string length matters

Never use a string that's too short. The extra limb stress can cause limb breakage, which is dangerous. A slightly too-long string can be twisted to shorten it. A too-short string should never be used.

Recurve and longbow string guide

Standard AMO string lengths

Adjusting brace height with string length

Brace height is critical for performance and safety. Each bow has a manufacturer-recommended brace height range (usually 1 inch variance). You can fine-tune brace height by:

• Adding twists: Shortens string, increases brace height (~1/8" per 5-10 twists)
• Removing twists: Lengthens string, decreases brace height
• Using different string length: Order 1" shorter/longer if twist adjustment isn't enough

Recommended brace heights by bow type:

• Recurve (hunting): 7.5" - 8.5"
• Recurve (Olympic/target): 8.5" - 9.25"
• Longbow (traditional): 6" - 7.5"
• Longbow (American flatbow): 6.5" - 7.5"

Always check your bow manufacturer's specs. Brace height that's too low causes arrow-string contact (bad accuracy, damaged fletchings). Too high reduces power and speed.

String materials for recurve/longbow

Important: Older bows and traditional longbows were designed for Dacron. Using low-stretch materials like Fast Flight on non-reinforced limbs can cause limb breakage. When in doubt, use Dacron B-50.

Shop custom recurve strings at Lancaster Archery or traditional bow strings at 3Rivers Archery.

Compound bow string and cable guide

Why compound strings are complex

Compound bows use precisely engineered string and cable systems to achieve let-off and cam synchronization. Unlike recurve strings where being off by 1/4" is acceptable, compound strings must be exact. Even 1/8" difference in string length can:

• Change draw length by 1/4" - 1/2"
• Affect cam timing (cams hit stops at different times)
• Reduce let-off percentage
• Create tuning problems (left/right impacts)
• Cause unusual wear patterns on cams

This is why measuring your old string accurately or using manufacturer specs is critical for compound bows.

Compound string components

Most modern compounds have a 2-cable system:

• Bowstring: Runs from cam to cam through cable guard
• Control cable (buss cable): Runs from bottom cam to top cam, controls synchronization
• Split cable (yoke): Y-shaped cable on top or bottom cam

Single-cam bows have only 1 cable. Older compounds may have different configurations. Always verify your bow's specific setup.

Typical compound string lengths by axle-to-axle

These are rough estimates. Always use manufacturer specs or measure your old string. Compounds have too much variation to rely on axle-to-axle alone.

How to order compound strings

When ordering from a custom string maker or manufacturer, provide:

• Bow make and model (e.g., "Mathews V3 31", "Hoyt RX-7", "PSE Evolve 35")
• Draw length setting (if adjustable)
• String material preference (BCY 452X, 8190, Trophy, etc.)
• Color preferences (main color, accent serving colors)
• Old string lengths if available (measured relaxed)

Most string makers have databases with specs for popular bow models. Providing bow model is more reliable than measurements for compounds.

String materials for compound bows

For hunting, BCY 452X is the gold standard - proven durability in all conditions. For competition, 8190 or X99 provide maximum performance. Avoid mixing materials (e.g., 452X string with Trophy cables) - use same material throughout for consistent stretch behavior.

Shop custom compound strings at Lancaster Archery.

When and how to replace bowstrings

Signs you need new strings NOW

• Broken strands: Any broken strand is immediate replacement - string can fail catastrophically
• Serving separation: Center serving or end serving coming apart exposes strands to abrasion
• Excessive stretch: Added 20+ twists and brace height still low
• Fraying or fuzz: More than light fuzz, especially near loops or cams
• String is 3+ years old: Even if it looks fine, materials degrade
• Dry rot: String stored in hot attic/car, feels brittle or crumbly
• Water damage: String got soaked and never properly dried

Installing new strings safely

Recurve bows:

1. Use a bow stringer - never bend bow by hand to string/unstring
2. Check string is not twisted before installing
3. Install string with proper loop orientation (small loop on top for most bows)
4. Check brace height with bow square after stringing
5. Shoot 20-30 arrows to let string settle, then recheck brace height
6. Add or remove twists to achieve manufacturer-spec brace height

Compound bows:

1. Use a bow press - never attempt to change strings without a press
2. Take photos before removing old strings (reference for cable routing)
3. Replace strings AND cables together (even if cables look OK)
4. Ensure cables are routed correctly through cable guard and slide
5. Check cam timing after installation (both cams should hit stops simultaneously)
6. Paper tune after string installation to verify arrow flight
7. Shoot 50-100 arrows to let strings settle, then check draw length and timing

If you're not comfortable using a bow press, take your bow to a shop. Incorrect string installation on compounds can cause tuning nightmares or damage.