About

Muzzle energy determines terminal performance. The kinetic energy of a projectile follows KE = 12mv², where small errors in velocity measurement propagate quadratically into the energy result. A 5% velocity error yields a 10.25% energy error. This tool computes kinetic energy, momentum, Taylor Knockout factor, and sectional density using exact unit conversion constants. It does not model drag, spin, or environmental factors. Results assume point-blank conditions with no energy loss to air resistance.

Hunters selecting cartridges for game at specific ranges, handloaders verifying load performance, and forensic analysts estimating impact forces all depend on accurate energy figures. Relying on approximate mental math or rounded conversion factors introduces systematic bias. This calculator uses the SAAMI-standard grain-to-gram factor of 0.06479891 and reports results to four significant figures. Note: Taylor KO factor requires bullet diameter input and applies primarily to dangerous-game cartridge comparison. Sectional density values below 0.200 generally indicate poor penetration on medium game.

Formulas

The primary calculation is the classical kinetic energy equation for a non-relativistic projectile:

KE = 12 m v²

Where KE is kinetic energy in J (joules), m is projectile mass in kg, and v is velocity in m/s. To convert to ft⋅lbf, divide joules by 1.3558179483.

Linear momentum:

p = m ⋅ v

Where p is momentum in kg⋅m/s.

Taylor Knockout Factor, an empirical index proposed by John "Pondoro" Taylor for comparing dangerous-game cartridges:

TKO = m_gr × v_fps × d_in7000

Where m_gr is mass in grains, v_fps is velocity in ft/s, and d_in is bullet diameter in inches. The constant 7000 converts grains to pounds.

Sectional Density:

SD = m_lbd_in²

Where m_lb is mass in pounds and d_in is bullet diameter in inches. Higher sectional density correlates with deeper penetration through tissue.

Unit conversion constants used: 1 grain = 0.06479891 g. 1 ft/s = 0.3048 m/s. 1 in = 25.4 mm. 1 J = 0.737562 ft⋅lbf.

Reference Data

Cartridge	Bullet Mass (gr)	Muzzle Velocity (fps)	Muzzle Energy (ft⋅lbf)	Diameter (in)	Taylor KO	Sectional Density
.22 LR	40	1080	104	0.224	1.38	0.114
9mm Luger	124	1150	364	0.355	7.23	0.141
.45 ACP	230	830	352	0.452	12.32	0.162
5.56×45 NATO	62	3020	1255	0.224	5.97	0.177
7.62×51 NATO	147	2800	2559	0.308	18.12	0.221
.308 Winchester	168	2650	2619	0.308	19.56	0.253
.30-06 Springfield	180	2700	2913	0.308	21.38	0.271
6.5 Creedmoor	140	2710	2283	0.264	14.32	0.287
.300 Win Mag	190	2900	3547	0.308	24.23	0.286
.375 H&H Mag	300	2530	4263	0.375	40.71	0.305
.416 Rigby	400	2400	5115	0.416	57.07	0.330
.458 Win Mag	500	2150	5132	0.458	70.29	0.341
.50 BMG	660	2910	12400	0.510	139.64	0.362
7mm Rem Mag	160	2950	3093	0.284	19.16	0.283
.243 Winchester	100	2960	1945	0.243	10.27	0.242
12 Gauge Slug	437.5	1560	2361	0.729	71.07	0.118

Frequently Asked Questions

Kinetic energy is proportional to the square of velocity (v²) but only linearly proportional to mass (m). Doubling bullet mass doubles energy, but doubling velocity quadruples it. This is why high-velocity rifle cartridges like 5.56×45 NATO (62 gr at 3020 fps) produce 1255 ft·lbf, exceeding the much heavier .45 ACP (230 gr at 830 fps) at 352 ft·lbf.

The commonly cited minimum for white-tailed deer is 1000 ft·lbf at point of impact, not at the muzzle. Energy decays with distance due to aerodynamic drag. A cartridge producing 1800 ft·lbf at the muzzle may fall below 1000 ft·lbf at 300 yards depending on ballistic coefficient. This calculator provides muzzle-only values. For range-specific energy, you need a ballistic trajectory solver that accounts for drag coefficient and atmospheric conditions.

Kinetic energy is a physics quantity measured in joules or foot-pounds. Taylor KO is an empirical index that incorporates bullet diameter, weighting frontal area alongside mass and velocity. Two cartridges with identical muzzle energy but different diameters will have different TKO values. The .458 Win Mag (500 gr, 0.458 in) scores TKO 70.29, while the .300 Win Mag (190 gr, 0.308 in) scores 24.23 despite comparable energy. Taylor KO was designed specifically for comparing cartridges against dangerous African game and has limited applicability outside that context.

Sectional density above 0.250 is generally considered adequate for medium-to-large game. Values above 0.300 are preferred for heavy or dangerous game where deep, straight-line penetration through bone and muscle is critical. The .375 H&H with a 300 gr bullet achieves SD 0.305. Low SD values (below 0.200) indicate a bullet that may fragment or deflect on heavy bone. Note that SD does not account for bullet construction. A bonded or solid bullet at SD 0.220 may outpenetrate a cup-and-core bullet at SD 0.280.

No. This calculator accepts user-supplied velocity as input and assumes it is the measured value at the muzzle. Barrel length significantly affects muzzle velocity. A 5.56×45 NATO round rated at 3020 fps from a 20-inch barrel may only achieve 2750 fps from a 14.5-inch barrel, reducing energy by approximately 17%. Always use chronograph-measured velocity for your specific firearm rather than manufacturer-published figures, which are typically measured from SAAMI-standard test barrel lengths.

The calculator displays results in both unit systems simultaneously. Internally, all calculations are performed in SI units (kilograms, meters per second, joules) and then converted. Key conversion factors: 1 J = 0.737562 ft·lbf. 1 kg·m/s = 7.23301 lb·ft/s. These conversions use exact NIST-defined factors with no rounding until the final display step.