# Foot Pounds of Energy Calculator

Calculate kinetic energy in foot-pounds from projectile weight and velocity. Convert to Joules and see momentum and USPSA power factor.

## What this calculates

Foot-pounds (ft-lbs) measure the kinetic energy of a moving projectile. A 150-grain bullet at 2,800 fps carries about 2,611 ft-lbs of energy. This calculator works for bullets, arrows, pellets, or any projectile where you know the weight in grains and the velocity in feet per second.

## Inputs

- **Projectile Weight** (gr) — min 0 — Weight of the projectile in grains (1 grain = 0.0648 grams).
- **Velocity** (fps) — min 0 — Velocity of the projectile in feet per second.

## Outputs

- **Kinetic Energy** (ft-lbs) — Kinetic energy in foot-pounds.
- **Kinetic Energy** (J) — Kinetic energy in Joules.
- **Momentum** (lb·s) — Momentum in pound-seconds.
- **Power Factor** — IPSC/USPSA power factor (weight × velocity / 1000).

## Details

**The formula:**

KE (ft-lbs) = (weight in grains × velocity in fps²) / 450,240

The constant 450,240 equals 2 × 7,000 (grains per pound) × 32.174 (gravitational acceleration in ft/s²). It converts the standard KE = 1/2 mv² formula into grain and fps units.

**Common reference values:**
- **.22 LR (40gr @ 1,080fps):** ~104 ft-lbs
- **9mm (124gr @ 1,150fps):** ~364 ft-lbs
- **.223 Rem (55gr @ 3,240fps):** ~1,282 ft-lbs
- **.308 Win (168gr @ 2,650fps):** ~2,620 ft-lbs
- **.30-06 (180gr @ 2,700fps):** ~2,914 ft-lbs
- **Crossbow bolt (400gr @ 400fps):** ~142 ft-lbs

**Energy vs. momentum:**

Energy grows with the square of velocity, so doubling speed quadruples energy. Momentum grows linearly with velocity. Both matter for terminal performance, but in different ways. Energy relates to tissue damage potential, while momentum relates to penetration depth.

**Archery note:** Arrows and crossbow bolts typically range from 250-500 grains at 150-400 fps, producing 30-150 ft-lbs. Even though this is much less than firearms, arrows achieve penetration through a different mechanism (cutting rather than expansion).

## Frequently Asked Questions

**Q: What does foot-pounds of energy mean?**

A: A foot-pound is the energy needed to lift one pound a distance of one foot against gravity. When applied to projectiles, it measures how much kinetic energy the projectile carries. Higher ft-lbs means the projectile can do more work on impact.

**Q: How many foot-pounds do you need for deer hunting?**

A: Most hunting guidelines recommend a minimum of 1,000 ft-lbs for deer at the point of impact. For elk and larger game, 1,500 ft-lbs or more is generally recommended. Keep in mind that energy drops with distance as the projectile slows down.

**Q: Why does velocity matter more than weight for energy?**

A: Because energy depends on velocity squared. Doubling the velocity quadruples the energy, while doubling the weight only doubles the energy. That is why light, fast bullets often carry more energy than heavier, slower ones of the same caliber.

**Q: Can I use this for arrows and crossbow bolts?**

A: Yes. Enter the arrow or bolt weight in grains and velocity in fps. A typical compound bow arrow weighs 350-500 grains at 250-330 fps, producing 55-100 ft-lbs. Crossbow bolts at 350-400 fps with heavier shafts can reach 100-150 ft-lbs.

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Source: https://vastcalc.com/calculators/physics/foot-pounds-of-energy
Category: Physics
Last updated: 2026-04-08