How do I calculate muzzle energy in foot-pounds?

Muzzle energy in ft-lb = (bullet mass in grains times velocity in fps squared) divided by 450,437. For example, a 150-grain bullet at 2,800 fps: (150 times 2800 squared) divided by 450,437 = (150 times 7,840,000) divided by 450,437 = 1,176,000,000 divided by 450,437 = 2,611 ft-lb. This formula uses the kinetic energy equation KE = 0.5 times mass times velocity squared, with grains and fps converted to consistent units.

How many foot-pounds is 1 BTU?

One BTU (British Thermal Unit) equals 778.169 foot-pounds of energy. To convert BTU to ft-lb, multiply BTU by 778.169. To convert ft-lb to BTU, divide by 778.169. For example, 1,000 ft-lb divided by 778.169 equals 1.285 BTU.

What is a good foot-pound rating for hunting?

Recommended minimum muzzle energies for hunting: whitetail deer 1,000 ft-lb, elk 1,500 ft-lb, moose and large game 2,000 ft-lb, small game 500 ft-lb. Many hunters prefer 1,500-2,500 ft-lb for deer-sized game to ensure reliable expansion and clean kills. At typical hunting ranges of 200-300 yards, energy drops significantly below muzzle figures.

How do I convert foot-pounds to calories?

To convert foot-pounds to calories (thermochemical), multiply ft-lb by 0.323832. To convert foot-pounds to kilocalories (kcal or food calories), multiply by 0.000323832. For example, 1,000 ft-lb times 0.323832 equals 323.8 calories (thermochemical) or 0.3238 kcal.

What is the difference between foot-pounds of energy and foot-pounds of torque?

Both use the same unit name and the same numerical calculation, but they measure different physical quantities. Foot-pounds of energy (or work) measures scalar energy: force times distance. Foot-pounds of torque measures rotational force: force times moment arm length. They are dimensionally equivalent but physically different. A torque of 100 ft-lb does not directly equal 100 ft-lb of work unless the object rotates through one radian.

How do I convert inch-pounds to foot-pounds?

Divide inch-pounds by 12 to get foot-pounds, since there are 12 inches in a foot. For example, 120 inch-pounds divided by 12 equals 10 foot-pounds. To convert foot-pounds to inch-pounds, multiply by 12. This conversion is common in automotive torque specifications, where smaller fasteners use inch-pounds and larger ones use foot-pounds.

What is the kinetic energy formula in foot-pounds?

Kinetic energy in foot-pounds = (mass in slugs times velocity in ft/s squared) divided by 2. Since 1 slug = 14.5939 lbm, you can also use: KE (ft-lb) = (mass in lbm times velocity in ft/s squared) divided by (2 times 32.174). For ballistics with grains and fps: KE (ft-lb) = (mass in grains times velocity in fps squared) divided by 450,437.

How many foot-pounds does a car engine produce?

A typical passenger car engine produces 150-300 ft-lb of peak torque. Compact cars average 150-200 ft-lb, family sedans 200-250 ft-lb, and performance vehicles 300-500 ft-lb. Heavy-duty diesel truck engines produce 800-2,000 ft-lb of torque. Sports cars like the Corvette Z06 produce around 460 ft-lb, while supercars like the Bugatti Chiron produce over 1,100 ft-lb.

Foot-Pounds of Energy Calculator

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Key conversion:
1 ft-lb = 1.35582 joules
1 ft-lb = 1.35582 Nm (torque)
1 BTU = 778.169 ft-lb
1 kWh = 2,655,224 ft-lb

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Sources & Methodology

✓ Conversion factors verified against NIST (National Institute of Standards and Technology) official unit conversion tables and Engineering Toolbox energy references.

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NIST — Weights and Measures Unit Conversion

The National Institute of Standards and Technology (NIST) is the US federal authority on measurement standards. All energy and torque conversion factors in this calculator (ft-lb to joules, BTU to ft-lb, etc.) use NIST-published exact or derived values to ensure maximum accuracy.

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Engineering Toolbox — Energy Units Converter

Engineering Toolbox provides widely-referenced conversion tables for energy units used in mechanical, thermal, and ballistic engineering. The ft-lb to kWh, calorie, and kcal factors used in this calculator are cross-referenced against Engineering Toolbox values for verification.

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SAAMI — Sporting Arms and Ammunition Manufacturers Institute

SAAMI sets industry standards for ammunition in the United States. The muzzle energy formula (grains times fps squared divided by 450,437) used in the muzzle energy tab is the SAAMI-accepted industry standard formula, derived from the kinetic energy equation KE = 0.5 times mass times velocity squared with units converted from grains and fps to consistent imperial units.

Methodology: All conversions use exact factors: 1 ft-lb = 1.35581795 J (exact NIST value). 1 BTU = 1,055.05585 J = 778.169 ft-lb. 1 cal (thermochemical) = 4.184 J = 3.08596 ft-lb. Muzzle energy formula: KE (ft-lb) = (mass in grains times velocity in fps squared) / 450,437. This constant (450,437) is derived from (2 times 32.174 ft/s squared times 7,000 grains/lb). For metric inputs, mass and velocity are converted to grains and fps before applying the formula.

⏱ Last reviewed: April 2026

Foot-Pounds of Energy — Complete Guide

The foot-pound (ft-lb or ft-lbf) is the standard imperial unit of energy and work, and also the standard unit of torque in the United States. Despite the metric system's global dominance, foot-pounds remain essential in American engineering, automotive specifications, firearms ballistics, and construction. Understanding how to calculate, convert, and apply foot-pound values is crucial for any engineer, mechanic, shooter, or DIY enthusiast working with US-standard equipment.

What Is a Foot-Pound of Energy?

One foot-pound of energy is the work done when a force of one pound-force (lbf) acts through a distance of one foot in the direction of the force. It is equivalent to 1.35582 joules in the SI system. The foot-pound appears in three main contexts in engineering practice:

Work/energy: The energy transferred when moving an object — for example, lifting a 1-pound weight by 1 foot requires 1 ft-lb of work
Torque: Rotational force measured as force times moment arm — engine output, fastener specifications, and impact wrench ratings all use ft-lb
Ballistic energy: Muzzle energy of firearms and kinetic energy of projectiles — used to evaluate stopping power and suitability for hunting

Key Foot-Pound Conversion Factors

1 ft-lb = 1.35582 J = 1.35582 Nm = 0.001285 BTU = 0.32383 cal

To joules: ft-lb × 1.35582 = joules
To Newton-meters: ft-lb × 1.35582 = Nm (same factor)
To BTU: ft-lb ÷ 778.169 = BTU
To calories: ft-lb × 0.323832 = cal (thermochemical)
To kcal: ft-lb ÷ 3085.96 = kcal (food calories)
To inch-pounds: ft-lb × 12 = in-lb

Muzzle Energy in Foot-Pounds

In firearms and ballistics, muzzle energy is the kinetic energy of a bullet at the moment it leaves the barrel, expressed in foot-pounds. It is the most commonly used measure of a cartridge's power. The formula is derived from the kinetic energy equation (KE = 0.5 × m × v²) adapted for the imperial units used in ballistics:

Muzzle Energy (ft-lb) = (Mass in grains × Velocity in fps²) / 450,437

The constant 450,437 = 2 × 32.174 (ft/s²) × 7,000 (grains/lb)
Example: 9mm 124gr at 1,150 fps: (124 × 1,150²) / 450,437 = (124 × 1,322,500) / 450,437 = 163,990,000 / 450,437 = 364 ft-lb

Muzzle Energy Reference Table by Cartridge

Cartridge	Bullet Weight	Velocity	Muzzle Energy	Typical Use
.22 LR	40 gr	1,200 fps	128 ft-lb	Small game, target
.380 ACP	95 gr	980 fps	203 ft-lb	Concealed carry
9mm Luger	124 gr	1,150 fps	364 ft-lb	Self-defense, duty
.40 S&W	165 gr	1,100 fps	443 ft-lb	Law enforcement
.45 ACP	230 gr	830 fps	352 ft-lb	Self-defense
.357 Magnum	125 gr	1,450 fps	583 ft-lb	Hunting, defense
.223 Remington	55 gr	3,240 fps	1,282 ft-lb	Varmint, target
.308 Winchester	168 gr	2,650 fps	2,620 ft-lb	Deer, long-range
30-06 Springfield	150 gr	2,910 fps	2,820 ft-lb	All North American game
.300 Win Mag	180 gr	2,960 fps	3,501 ft-lb	Large game, elk, moose

Torque Specifications in Foot-Pounds

In automotive and mechanical engineering, torque is almost universally specified in ft-lb in the United States. Engine output, lug nut torque, head bolt torque, and impact wrench ratings all use ft-lb. When working with metric-spec fasteners and European equipment, you must convert between ft-lb and Newton-meters (Nm). The conversion factor is straightforward: 1 ft-lb = 1.35582 Nm, and 1 Nm = 0.73756 ft-lb.

Common automotive torque specifications: lug nuts (compact car) 80-100 ft-lb, lug nuts (truck) 100-150 ft-lb, spark plugs 12-25 ft-lb, oil drain plug 15-30 ft-lb, cylinder head bolts 60-90 ft-lb, connecting rod bolts 35-50 ft-lb.

💡 Important: Foot-pounds of torque and foot-pounds of energy share the same unit name and conversion factors, but they measure fundamentally different physical quantities. Torque is a rotational force vector; energy is a scalar quantity. The numerical values are only equivalent when a torque acts through exactly one radian of rotation. Never add or directly compare torque ft-lb values with energy ft-lb values.

Frequently Asked Questions

A foot-pound (ft-lb) is an imperial unit of energy equal to the work done when a force of one pound-force moves an object one foot in the direction of the force. It equals 1.35582 joules. The foot-pound is used to measure mechanical work, kinetic energy of projectiles, and engine/fastener torque throughout the United States.

Multiply foot-pounds by 1.35582 to get joules. For example, 100 ft-lb times 1.35582 equals 135.58 joules. To convert joules back to foot-pounds, divide by 1.35582. This is the exact NIST-published conversion factor.

Use the formula: Muzzle Energy (ft-lb) = (mass in grains times velocity in fps squared) / 450,437. The constant 450,437 converts grains and fps to consistent imperial units. Example: a 150-grain bullet at 2,910 fps gives (150 times 2910 squared) / 450,437 = 2,820 ft-lb. Our muzzle energy calculator tab handles any mass and velocity unit combination automatically.

Multiply foot-pounds by 1.35582 to get Newton-meters. For example, 100 ft-lb equals 135.58 Nm. To convert Nm to ft-lb, multiply by 0.73756. This conversion is identical to the joule conversion because Nm and J are dimensionally equivalent. It is widely used when working between US-spec and European torque specifications.

One BTU (British Thermal Unit) equals 778.169 foot-pounds of energy. To convert BTU to ft-lb, multiply by 778.169. To convert ft-lb to BTU, divide by 778.169. For example, 1,000 ft-lb divided by 778.169 equals 1.285 BTU. BTU is commonly used in HVAC and heating system ratings.

Most hunting authorities recommend a minimum of 1,000 ft-lb at the point of impact for deer-sized game. Common deer hunting cartridges like the .308 Winchester deliver 2,620 ft-lb at the muzzle and still retain over 1,500 ft-lb at 300 yards. For elk and larger game, 1,500 ft-lb at impact is the commonly recommended minimum, requiring cartridges like .300 Win Mag or larger.

To convert foot-pounds to thermochemical calories, multiply ft-lb by 0.323832. For food calories (kilocalories, kcal), divide by 3,085.96. For example, 1,000 ft-lb times 0.323832 equals 323.8 thermochemical calories, or 0.3238 food calories. Foot-pounds are rarely used in nutrition contexts, but the conversion is useful in thermodynamics and physics problems.

Both use the foot-pound unit, but they measure different things. Energy ft-lb is a scalar (amount of work done). Torque ft-lb is a rotational force vector (force times distance from pivot). They share the same numerical conversion factors to metric units (1 ft-lb = 1.35582 joules for energy; 1 ft-lb = 1.35582 Nm for torque), but you cannot directly add or equate an energy value in ft-lb with a torque value in ft-lb.

Divide inch-pounds by 12 to get foot-pounds, because there are 12 inches in a foot. For example, 120 in-lb divided by 12 equals 10 ft-lb. To convert ft-lb to in-lb, multiply by 12. This is common in automotive work: small fasteners like spark plugs and oil pan bolts are often specified in in-lb, while larger fasteners like lug nuts and head bolts use ft-lb.

For objects in everyday units: KE (ft-lb) = (mass in lbm times velocity in ft/s squared) / (2 times 32.174). The 32.174 is the gravitational constant in ft/s squared. For ballistics using grains and fps, the simplified formula is KE (ft-lb) = (grains times fps squared) / 450,437. For metric inputs, convert kg to lbm (times 2.20462) and m/s to fps (times 3.28084) first.

A typical compact car produces 150-200 ft-lb of peak torque. Family sedans average 200-280 ft-lb. Performance V8 engines produce 350-500 ft-lb. Heavy-duty diesel pickup trucks produce 800-1,200 ft-lb of torque. Industrial diesel engines for heavy equipment can produce over 2,000 ft-lb. Sports cars and supercars range from 400 ft-lb to over 1,100 ft-lb for the most powerful production vehicles.

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