Convert foot-pounds to joules, BTU, calories, and kWh. Ballistic muzzle energy calculator from projectile mass and velocity with common cartridge comparison table.
The foot-pound (ft·lbf) is a unit of energy equal to the work done when a force of one pound moves an object through a distance of one foot. Equivalent to approximately 1.3558 joules, it remains widely used in the United States for mechanical and ballistic applications.
In firearms and ballistics, muzzle energy — the kinetic energy of a projectile as it leaves the barrel — is almost universally quoted in foot-pounds. This energy is calculated using E = ½mv², with mass measured in grains (1 grain = 64.8 mg) and velocity in feet per second. A 9mm pistol round carries about 355 ft·lbs, while a .308 Winchester rifle round delivers nearly 2,650 ft·lbs.
This calculator provides bidirectional conversion between foot-pounds and five other energy units (joules, BTU, calories, kWh, eV), includes a dedicated ballistic muzzle energy calculator, and features a comparison table of common cartridge energies. Check the example with realistic values before reporting.
Energy unit conversions involve memorizing conversion factors across imperial and metric systems. This calculator handles six units simultaneously, includes a dedicated ballistic calculator using grains and fps, and provides visual comparisons to contextualize energy values. Keep these notes focused on your operational context. Tie the context to the calculator’s intended domain. Use this clarification to avoid ambiguous interpretation.
Energy Conversion: 1 ft·lbf = 1.3558 J Ballistic Muzzle Energy: E = ½mv² In imperial: E (ft·lbs) = (mass in grains × velocity² in fps) / 450,437 Other conversions: 1 BTU = 1,055.06 J = 778.16 ft·lbs 1 cal = 4.184 J = 3.086 ft·lbs 1 kWh = 3,600,000 J = 2,655,224 ft·lbs
Result: 355 ft·lbs = 481.3 J
355 ft·lbs × 1.3558 J/ft·lbs = 481.3 J. Ballistic check: E = (115 × 1180²) / 450437 ≈ 355.5 ft·lbs, confirming the 9mm Luger specification.
The foot-pound-force (ft·lbf) quantifies the energy transferred when a one-pound force displaces an object by one foot in the direction of the force. In SI units, 1 ft·lbf = 1.3558179483 J. Despite the metric system's global adoption, foot-pounds remain standard in American engineering, HVAC, and firearms contexts.
Muzzle energy is critical in firearms selection for hunting, self-defense, and target shooting. Hunting regulations in many jurisdictions specify minimum muzzle energy thresholds — for example, many states require at least 1,000 ft·lbs for deer hunting. The .308 Winchester (2,648 ft·lbs) and .30-06 Springfield (2,820 ft·lbs) comfortably exceed this, while handgun rounds (300-500 ft·lbs) generally do not.
A useful way to grasp energy scales: a 9mm bullet (355 ft·lbs ≈ 481 J) carries roughly the same kinetic energy as a 1 kg object dropped from 49 meters. A food Calorie (kcal) at 4,184 J is equivalent to about 9 such bullets. And a single gallon of gasoline contains about 120 MJ — the energy equivalent of approximately 88 million foot-pounds.
They are the same unit. The 'f' in ft·lbf explicitly indicates force (pound-force), distinguishing it from ft·lb which can sometimes be confused with pound-mass × feet. Both refer to the energy unit equal to 1.3558 joules.
The US firearms industry standardizes on imperial units. Projectile mass is measured in grains (a traditional apothecaries' unit, 1 grain = 64.8 mg) and velocity in feet per second, making foot-pounds the natural energy unit.
Muzzle energy is only one factor. Terminal ballistics also depends on bullet construction, expansion, penetration depth, and shot placement. Two rounds with identical muzzle energy can have very different terminal performance.
A grain is a unit of mass equal to 64.79891 mg (about 1/7000 of a pound). It was originally based on the weight of a single grain of wheat or barleycorn and is still the standard unit for ammunition weights.
Horsepower is a power unit (energy/time), not an energy unit. One horsepower = 550 ft·lbs per second. To convert energy to power, divide ft·lbs by the time in seconds: P (hp) = E (ft·lbs) / (550 × t).
The eV is the standard energy unit in atomic and particle physics. Including it allows cross-scale comparison from everyday (ft·lbs, BTU) through electrical (kWh) to subatomic (eV) energy scales.