Arrow Speed Calculator
Enter your bow's IBO speed rating, draw weight, arrow weight, and shaft length to calculate the estimated arrow speed. Also computes FOC (Front of Center) balance and kinetic energy for arrow selection.
Arrow Speed Calculator
Calculate FPS, FOC, and kinetic energy
Arrow speed is derived from the IBO (International Bowhunting Organization) standard: Base speed of 300 fps with a 350-grain arrow shot from a 30-inch draw length and 70 lb draw weight. Adjustments are made for actual draw weight, arrow weight, and distance from the bow's bridge to the nock.
How Arrow Speed Calculation Works
The arrow speed formula is based on the IBO (International Bowhunting Organization) standard, which defines a baseline speed of 300 ft‑per‑second (fps) under specific conditions: a 350‑grain arrow, a 30‑inch draw length, and a 70‑lb draw weight. Adjustments are then made for the actual specifications of the bow and arrow.
**IBO Baseline**: 300 fps with 350‑grain arrow, 30‑inch draw, 70‑lb draw weight.
**Adjustment Factors**: 1. **Distance from bridge to nock**: The IBO test uses a standard 7‑inch distance. For every inch above or below 7 inches, the speed is adjusted by 10 fps (subtracting if longer, adding if shorter). This accounts for the energy stored in the bow's limbs and how the draw length affects the power stroke. 2. **Weight over IBO**: The IBO standard uses 5 grains per inch (GPI) × shaft length. If your arrow is heavier or lighter than this, the speed is adjusted. The formula subtracts ((Arrow Weight - 5 × GPI × Shaft Length) × 1.4) / 1000 from the IBO speed. Heavier arrows slow the bow down; lighter arrows speed it up. 3. **Draw weight**: A heavier draw weight generally increases arrow speed, but the IBO adjustment formula primarily accounts for arrow weight. The calculator uses the entered draw weight for FOC and KE calculations.
**FOC (Front of Center) Balance**: - FOC measures how far forward the arrow's center of gravity is, expressed as a percentage of the total arrow length. - Formula: FOC % = (Distance from nock to balance point - (Arrow Length ÷ 2)) ÷ Arrow Length × 100. - A typical FOC for target arrows is 7-10%; for hunting arrows, 10-15% is common for better flight stability.
**Kinetic Energy (KE)**: - KE measures the energy delivered by the arrow upon impact, which is critical for hunting effectiveness. - Formula: KE = (Arrow Weight × Arrow Speed²) ÷ 450,240, where weight is in grains and speed is in fps, giving KE in foot‑pounds (ft‑lb). - Higher KE generally means better penetration for large game. Minimum KE recommendations: 25-40 ft‑lb for small game, 40-60 ft‑lb for medium game (deer, elk), 65+ ft‑lb for large game (bear, moose).
- IBO baseline adjustment logic
- FOC balance calculation
- Kinetic energy formula for hunting
- Typical KE ranges by game type
Worked Example
Example: Calculate arrow speed and FOC for a typical hunting setup.
Settings: - IBO speed: 300 fps (standard) - Draw weight: 60 lb - Arrow weight: 400 grains - Shaft length: 30 inches - Bridge-to-nock distance: 7 inches (default)
**Step 1**: Arrow Speed = IBO - (Distance × 10) - ((Arrow Weight - 5 × GPI × Shaft Length) × 1.4 / 1000) - The GPI (grains per inch) is not directly entered; the formula uses a simplified assumption. If we assume a typical GPI of 9.5 for a 30‑inch shaft: 5 × 9.5 × 30 = 1,425 grains (this is the IBO reference weight). - Arrow Weight - Reference Weight = 400 - 1,425 = -1,025 - (-1,025) × 1.4 / 1000 = -1.435 - Arrow Speed = 300 - (7 × 10) - (-1.435) = 300 - 7 + 1.435 ≈ 294.4 fps
**Step 2**: FOC calculation. - Assume the balance point is at 19 inches from the nock on a 28‑inch arrow. - FOC % = (19 - (28 ÷ 2)) ÷ 28 × 100 = (19 - 14) ÷ 28 × 100 = 5 ÷ 28 × 100 ≈ 17.9%
**Step 3**: Kinetic Energy. - KE = (400 × 294.4²) ÷ 450,240 = (400 × 86,671.36) ÷ 450,240 = 34,668,544 ÷ 450,240 ≈ 77 ft‑lb
**Result**: ~294 fps arrow speed, ~18% FOC (hunting‑style balance), ~77 ft‑lb kinetic energy (adequate for medium‑sized game like deer).
**The calculator displays each step with the formula substitution and the intermediate results, so you can verify the math independently.**
IBO Speed Adjustments: Quick Reference
- **Every inch of bridge‑to‑nock over 7″ subtracts 10 fps**. Every inch under 7″ adds 10 fps. - **Every 5 grains over the IBO reference weight (5 × GPI × shaft length)** subtracts ~1 fps (the 1.4 factor and ÷1000 make it a small adjustment for typical arrow weights). - **Example**: A 400‑grain arrow vs. the IBO reference of ~1,425 grains (for a 30‑inch, 9.5 GPI shaft) is 1,025 grains heavier, which would theoretically reduce speed by about 1.4 fps - but the IBO formula is designed around the reference weight, so the actual speed reduction from weight alone is modest. The bigger speed factors are bridge‑to‑nock distance and, in practice, the bow's actual performance chronographed over chronograph.
**Why the IBO standard exists**: It provides a common baseline so archers can compare bows. However, real-world arrow speed is best determined by chronographing (shooting through a chronograph) your specific bow and arrow combination. This calculator provides a reliable estimate for selection and comparison purposes.
FOC Guidelines by Archery Style
- **Target arrows (7-10% FOC)**: Optimized for flat trajectory and minimal wind drift. Common in Olympic recurve and target compound setups. - **Hunting arrows (10-15% FOC)**: More front‑heavy for better stability and penetration, especially broadhead‑ tipped arrows. The added forward weight counters the drag of a broadhead. - **3D/Field arrows (10-12% FOC)**: A compromise between target flatness and hunting stability.
**How to adjust FOC**: - To increase FOC: add weight to the front (inserts, heavier broadheads, weighting the tip). - To decrease FOC: add weight to the rear (nock, fletching, insert adjustments).
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Open calculator →Frequently Asked Questions
What is a good IBO speed for a bow?
IBO speeds vary widely by bow design, limb technology, and cam system. Modern compound bows range from 300 to 370+ fps. A higher IBO number indicates a faster bow (all else equal), but actual arrow speed depends on your arrow weight and setup. For hunting, a practical IBO range is 310-340 fps. For target shooting, 290-320 fps is common and often more forgiving.
Does arrow length affect speed?
Yes. The IBO formula explicitly adjusts for bridge‑to‑nock distance (typically 7 inches). A longer draw length (bridge‑to‑nock > 7″) reduces the claimed IBO speed by 10 fps per inch, because the power stroke is shorter relative to the draw. Conversely, a shorter draw length increases the effective speed. Arrow shaft length also affects the FOC balance and the weight‑over‑IBO adjustment.
What FOC should I shoot for hunting?
For hunting with broadheads, 10-15% FOC is recommended. This provides enough forward stability to keep the arrow flying straight broadhead‑first, even in wind, and ensures the energy is delivered to the target rather than lost to arrow oscillation. Target shooters often prefer 7-10% FOC for a flatter trajectory.
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