Formula used
The calculator uses kinetic energy:
E = ½ · m · v²
where m is mass and v is velocity.
- E in joules (J) when using kilograms and meters/second.
- Converted to foot‑pounds using 1 ft·lbf = 1.355817948 J.
- Shortcut (grains + ft/s): E(ft·lbf) = w(gr) · v² / 450240.
How to use this calculator
- Enter the bullet mass (or weight) and choose its unit.
- Enter velocity and choose the correct speed unit.
- Select decimal places for the displayed results.
- Optionally enable steps to see conversions and math.
- Click Calculate, then export using CSV or PDF.
Example data table
| Case | Weight (gr) | Velocity (ft/s) | Energy (ft·lbf) | Energy (J) |
|---|---|---|---|---|
| Example A | 55 | 3200 | 1250.9 | 1696.0 |
| Example B | 124 | 1150 | 364.2 | 493.8 |
| Example C | 180 | 1000 | 399.8 | 542.0 |
| Example D | 40 | 1800 | 287.8 | 390.3 |
| Example E | 230 | 900 | 413.8 | 561.0 |
Bullet energy guide (data notes)
1) Weight inputs: grains, grams, ounces, pounds
Five mass units are accepted and converted to kilograms for the main equation. Useful references: 1 grain = 0.06479891 g and 7000 grains = 1 lb. Entering 124 gr becomes about 0.00803 kg internally, for consistent comparisons today.
2) Velocity inputs: ft/s, m/s, mph, km/h
Speed is converted to m/s using fixed factors: 1 ft/s = 0.3048 m/s, 1 mph = 0.44704 m/s, and 1 km/h = 0.27778 m/s. Example: 1150 ft/s ≈ 350.52 m/s.
3) Energy output: joules and foot‑pounds
Energy is computed in joules, then converted to foot‑pounds using 1 ft·lbf = 1.355817948 J. As a quick check, 500 J ≈ 368.7 ft·lbf.
4) The classic grains + ft/s shortcut
With grains and ft/s, you can also use E(ft·lbf) = w(gr) · v² / 450240. The constant 450240 bundles the unit conversions and the ½ factor.
5) Velocity dominates because v is squared
Energy scales with v². At 124 gr, 1000 ft/s gives ~275.4 ft·lbf, while 2000 ft/s gives ~1101.6 ft·lbf—four times higher.
6) Momentum is also reported
Momentum uses p = m · v (kg·m/s) and grows linearly with speed. In the examples, 124 gr at 1150 ft/s is about 2.816 kg·m/s.
7) Reading the example range on this page
The built‑in table spans about 288–1251 ft·lbf (390–1696 J). Use it to sanity‑check inputs, not as a safety guarantee. Follow local laws and safe handling practices.
FAQs
1) Why does the energy jump so much with speed?
Energy uses E = ½mv². Because velocity is squared, a 10% speed increase raises energy by about 21%. Small measurement errors in speed can noticeably change results.
2) Can I enter mass in grams or ounces?
Yes. Select grams, ounces, pounds, kilograms, or grains. The calculator converts everything to kilograms internally, then converts the final energy back to foot‑pounds and joules for display.
3) What is the 450240 constant?
It is a shortcut constant used when weight is in grains and speed is in ft/s. It bundles unit conversions plus the ½ factor, so the output lands directly in foot‑pounds.
4) Is this the same as muzzle energy?
This tool computes kinetic energy at whatever speed you enter. If your speed is a muzzle velocity measurement, then the result matches muzzle energy for that projectile.
5) Why show momentum too?
Momentum (m·v) helps compare how “pushy” two cases are, especially when masses differ. It changes linearly with speed, unlike energy, which changes with speed squared.
6) Are results exact?
No. They depend on input quality and rounding. Published speeds can vary by barrel length, temperature, and measurement method. Use this as an estimate for education and comparison.