Recoil Velocity Calculator

How it works

1. 1Enter the projectile’s mass and muzzle (exit) velocity, then the mass of the recoiling body (rifle, cannon, launcher).
2. 2The calculator converts inputs to SI and applies conservation of momentum: v_recoil = −(m_p · v_p) ÷ m_body.
3. 3The result is the recoil speed; the body always moves opposite to the projectile, keeping total momentum zero.

Use cases

• Firearms design — estimating felt recoil to compare cartridge and rifle combinations.
• Artillery and rocketry — sizing recoil-absorption mechanisms for heavy launchers.
• Physics education — demonstrating Newton’s third law and momentum conservation.

Frequently asked questions

What formula does this calculator use?

Conservation of momentum from rest: m_p·v_p + m_body·v_recoil = 0, so v_recoil = −(m_p·v_p) ÷ m_body. The minus sign means the body moves opposite to the projectile. A 0.01 kg bullet at 400 m/s from a 4 kg rifle gives −1 m/s — the rifle moves back at 1 m/s.

Why is the result shown as a magnitude?

The formula returns a negative value because recoil is opposite to the projectile. Since the positive direction is arbitrary, the tool shows the speed magnitude and states the direction in words.

Does it account for propellant gas or friction?

No. The model assumes a rigid system firing from rest and ignores ejected gas mass, friction, and recoil mechanisms. Real recoil is slightly higher because expanding gases also carry momentum. It is a good first-order estimate.