What this calculator does
A firearm recoils because the bullet leaves the barrel with momentum in one direction, and something has to carry the equal and opposite momentum the other way. This recoil calculator uses the simplest version of that idea, conservation of momentum between the bullet and the firearm, to estimate how fast the firearm moves backward and how much energy that motion carries.
This is a simplified model, not a full ballistics calculation. It treats the bullet as the only thing gaining forward momentum, when in reality the burning powder charge also leaves the muzzle as high-speed gas and adds a further push. Free recoil measured on a proper test rig is typically somewhat higher than this figure as a result, so treat the result here as a useful comparison between loads, not a lab-grade measurement.
The formula
Bullet weight is converted from grains to pounds (7,000 grains to the pound), then recoil velocity follows from momentum conservation: the bullet's mass times its velocity equals the firearm's mass times its recoil velocity, so recoil velocity is that product divided by the firearm weight. Recoil energy then follows the standard kinetic energy formula, using the firearm's mass in slugs (its weight divided by the acceleration of gravity, 32.174 ft/s²).
| Term | Meaning |
|---|---|
| Bullet weight | The mass of the projectile alone, in grains, as printed on ammunition boxes. |
| Bullet velocity | Muzzle velocity, the speed the bullet leaves the barrel at, in feet per second. |
| Firearm weight | The total weight of the firearm as fired, including any scope or accessories attached. |
| Recoil velocity | How fast the firearm itself moves backward immediately after firing. |
| Recoil energy | The kinetic energy of that backward motion, felt as the "kick" against the shoulder or hand. |
The inputs explained
| Field | What to enter |
|---|---|
| Bullet weight (grains) | The bullet weight in grains, found on the ammunition box. |
| Bullet velocity (muzzle velocity) (ft/s) | The muzzle velocity in feet per second, also usually printed on the ammunition box or found in load data. |
| Firearm weight (lb) | The firearm weight as actually fired, in pounds, including any accessories. |
When to use it
Comparing two loads in the same firearm
Holding firearm weight fixed and changing bullet weight or velocity shows how much a heavier bullet or a hotter load increases felt recoil, before buying a case of either.
Choosing a firearm weight for a given cartridge
Working the other way, a heavier firearm reduces recoil velocity and energy for the same cartridge, which is why many hard-kicking rifles are built heavy on purpose.
Explaining why two similar cartridges feel different
Two loads with the same bullet weight but different velocities, or the same velocity but different bullet weights, can produce noticeably different recoil, and this makes the difference explicit rather than anecdotal.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How recoil changes with bullet weight, same velocity and firearm
The same muzzle velocity and firearm weight, across a range of bullet weights.
| Bullet weight | Recoil velocity | Recoil energy |
|---|---|---|
| 100 gr | 5.00 ft/s | 3.11 ft-lb |
| 130 gr | 6.50 ft/s | 5.25 ft-lb |
| 150 gr | 7.50 ft/s | 6.99 ft-lb |
| 165 gr | 8.25 ft/s | 8.46 ft-lb |
| 180 gr | 9.00 ft/s | 10.07 ft-lb |
| 200 gr | 10.00 ft/s | 12.43 ft-lb |
How recoil changes with firearm weight, same cartridge
A fixed bullet weight and velocity, fired from firearms of different weights.
| Firearm weight | Recoil velocity | Recoil energy |
|---|---|---|
| 6 lb | 10.00 ft/s | 9.32 ft-lb |
| 7 lb | 8.57 ft/s | 7.99 ft-lb |
| 8 lb | 7.50 ft/s | 6.99 ft-lb |
| 9 lb | 6.67 ft/s | 6.22 ft-lb |
| 10 lb | 6.00 ft/s | 5.59 ft-lb |
| 12 lb | 5.00 ft/s | 4.66 ft-lb |
Questions
Why does this recoil calculator give a lower number than my chronograph or a recoil chart?
This is a simplified free-recoil estimate based only on bullet momentum. It leaves out the momentum of the propellant gas leaving the muzzle, which adds further recoil, so a full calculation or a measured test typically comes out somewhat higher, especially for cartridges with a large powder charge relative to bullet weight.
Does a muzzle brake change this result?
No, this calculator estimates free recoil before any muzzle device. A muzzle brake redirects propellant gas to reduce felt recoil, which is a separate effect this simplified momentum calculation does not model.
What is the difference between recoil velocity and recoil energy?
Recoil velocity is how fast the firearm moves backward. Recoil energy is the kinetic energy of that motion, which depends on both the velocity and the firearm's own weight, and is the figure most often used to compare how much a given firearm and load will "kick".
Should shoulder-mounted and handheld firearms be compared the same way?
The physics is the same, but felt recoil also depends on how the firearm is held and braced, stock design, grip and recoil pads, none of which this calculator can account for. Use it to compare loads and firearm weights, not to predict exactly how a given shooter will feel it.
For general projectile motion and speed conversions elsewhere in ballistics, see the RPM converter for rotational speed figures.