Bow Efficiency Calculator
Bow efficiency is the share of the energy stored in the limbs that ends up in the arrow. Estimate stored energy from your draw weight and power stroke, enter a chronograph speed, and see how efficient your setup really is.
🎯 Bow Efficiency Calculator
Enter your values below. Results update as you type.
Power stroke = Draw length − Brace height − 1.75 in
Stored energy ≈ Draw weight × Power stroke ÷ 12 × Curve factor
Efficiency = Arrow KE ÷ Stored energy, where KE = grains × fps² ÷ 450,800
The curve factor reflects how much area sits under the draw-force curve. A measured force-draw curve always beats the estimate.
📊 Typical Bow Efficiency
Typical ranges with a correctly matched arrow. Heavier arrows almost always raise efficiency.
| Bow Type | Typical Efficiency | Notes |
|---|---|---|
| Modern compound | 75–85% | Highest with heavier arrows and well-timed cams |
| Recurve | 70–80% | Lighter limbs and string materials help |
| Longbow | 65–75% | Heavier limb tips absorb more energy |
| Very light arrow (any bow) | Below 70% | More energy goes into vibration and noise |
📘 Worked Example
A 70 lb compound with a 29 in draw and 6 in brace height has a power stroke of 29 − 6 − 1.75 = 21.25 in. Estimated stored energy is 70 × 21.25 ÷ 12 × 0.82 ≈ 101.6 ft-lb.
A 425-grain arrow measured at 290 fps carries 425 × 290² ÷ 450,800 ≈ 79.3 ft-lb. Efficiency is 79.3 ÷ 101.6 ≈ 78%, right in the normal range for a hunting compound.
Why efficiency rises with arrow weight
The limbs, cams, and string have to accelerate their own mass as well as the arrow. A heavier arrow takes a larger share of the stored energy, so less is left over as vibration and noise. That is why heavy hunting arrows feel quieter and why dry-firing (no arrow) is so destructive.
❓ Frequently Asked Questions
What is bow efficiency?
It is the percentage of the energy stored in the drawn bow that becomes arrow kinetic energy. The rest is lost to limb, cam, and string movement, vibration, and sound.
What is a good efficiency for a compound bow?
Most modern compounds land between 75% and 85% with a reasonably heavy arrow. Results above 90% usually mean a speed or draw weight reading is off.
How do I measure stored energy exactly?
Draw the bow in 1-inch steps with a scale, record the force at each step, and add up the area under the curve. The result in inch-pounds divided by 12 gives stored energy in ft-lb.
How can I make my bow more efficient?
Shoot a heavier arrow, keep cams in time, and remove unnecessary string accessories. Each change shifts more of the stored energy into the arrow.
🧮 Related Calculators
Calculator results are planning estimates. Always confirm your setup with chronograph readings and real shooting.