Unit Conversion Calculator — Amps, Torque, Pressure, Power

Convert amps to watts, ft-lb to joules/N·m, MPa/bar to PSI, kW to HP, and PSI to kPa — bidirectional, with exact NIST conversion factors.

July 12, 2026

Conversion

Voltage (V)

Current (Amps)

Power (Watts)

Watts = Amps × Volts. Unlike the other conversions on this tool, amps-to-watts isn't a fixed multiplier — it depends on voltage, since watts measure real power and amps only measure current flow. This formula applies to DC circuits or purely resistive AC loads (heaters, incandescent bulbs, resistive elements). Motors, transformers, and other reactive AC loads need a power-factor term (Watts = Amps × Volts × Power Factor) for an exact figure.

Enter a value on either side and the other side updates instantly — every pair here works in both directions. Six of these seven conversions (everything except Amps ↔ Watts) use a fixed multiplier from NIST's Guide to the SI; Amps ↔ Watts is a formula (P = V × I) because electrical power depends on voltage, not just current.

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Reference Values

Last verified: Jul 11, 2026

Category	Range	What It Means	Status
Amps → Watts	Watts = Amps × Volts	Not a fixed multiplier — power depends on voltage. Formula shown is for DC or purely resistive AC loads; motors and other reactive AC loads need a power-factor term for exact wattage.	Good
Foot-Pounds → Joules (Energy)	1 ft-lb = 1.35582 J	Energy or work conversion — how much a force moving a distance is worth in metric joules.	Good
Foot-Pounds → Newton-Meters (Torque)	1 ft-lb = 1.35582 N·m	Same numeric factor as the energy conversion, but a different physical quantity — torque, not energy. Mislabeling the two is a common mistake.	Good
Newton-Meters → Foot-Pounds (Torque) ★	1 N·m = 0.737562 ft-lb	The inverse torque conversion — commonly used for torque wrench specs on lug nuts, bolts, and fasteners.	★ Best
MPa → PSI	1 MPa = 145.038 psi	Megapascals to pounds per square inch — used for concrete compressive strength, material tensile strength, and hydraulic ratings.	Good
Bar → PSI ★	1 bar = 14.5038 psi	Common for tire pressure, air compressors, and hydraulic systems specified in bar outside the US.	★ Best
kW → HP	1 kW = 1.34102 hp	Mechanical (imperial) horsepower — the standard conversion used for motor, engine, and generator power ratings.	Good
PSI → kPa	1 psi = 6.89476 kPa	Pounds per square inch to kilopascals — used for tire pressure specs, medical device pressure readings, and general engineering pressure conversions.	Good

Source: NIST Special Publication 811, Guide to the SI, Appendix B (conversion factors); MechaniCalc Unit Conversion Factors reference. Amps-to-watts is derived from the basic power formula (P = V × I), not a lookup table.

Worked Examples

Amps to Watts (Household Circuit)

Current: 15 A
Voltage: 120 V

1,800 W

Watts = Amps × Volts = 15 × 120 = 1,800 W. This is why a 15A/120V circuit is generally rated for about 1,800W of continuous resistive load (with code typically capping continuous use at 80% of that).

Foot-Pounds to Joules (Energy)

Energy: 50 ft-lb
Mode: Energy

67.79 J

50 × 1.35582 = 67.791 J. Same factor would apply if this were torque instead, but the unit would be N·m, not joules — the mode toggle exists because the two quantities aren't interchangeable despite sharing a conversion number.

Newton-Meters to Foot-Pounds (Lug Nut Torque)

Torque: 100 N·m

73.76 ft-lb

100 × 0.737562 = 73.7562 ≈ 73.76 ft-lb — a typical passenger car lug nut torque spec, commonly quoted in both units depending on the torque wrench.

MPa to PSI (Concrete Strength)

Pressure: 25 MPa

3,625.95 psi

25 × 145.038 = 3,625.95 psi — close to the commonly specified 3,600 psi compressive strength for standard structural concrete.

Bar to PSI (Tire Pressure)

Pressure: 2.2 bar

31.91 psi

2.2 × 14.5038 = 31.908 ≈ 31.91 psi — within the typical 30–35 psi passenger car tire pressure range.

kW to HP (Motor Rating)

Power: 75 kW

100.58 hp

75 × 1.34102 = 100.5765 ≈ 100.58 hp — a 75kW electric motor is commonly marketed as a "100 hp" motor using this mechanical horsepower conversion.

How to Use This Calculator

1

Pick a conversion pair

Choose from Amps ↔ Watts, Foot-Pounds ↔ Joules/N·m, N·m ↔ Foot-Pounds, MPa ↔ PSI, Bar ↔ PSI, kW ↔ HP, or PSI ↔ kPa from the dropdown.
2

For Amps ↔ Watts, enter Voltage first

This is the one pair that needs a third number — power depends on voltage, so enter your circuit's voltage before reading amps or watts.
3

For Foot-Pounds, choose Energy or Torque mode

Foot-pounds means two different physical quantities depending on context. Pick Energy if you're measuring work/energy (converts to joules) or Torque if you're measuring a rotational force (converts to N·m).
4

Enter a value on either side

Type into either input box — the other one updates instantly using the exact conversion factor for that pair, in either direction.
5

Read the formula and note below the result

Each pair shows its exact multiplier and a short explanation of what the units actually measure, so you can double-check you picked the right conversion.

What Each Value Means

Watts (W): The SI unit of power — the rate at which energy is used or delivered. Calculated for resistive circuits as Amps × Volts.
Foot-Pounds (ft-lb) (ft-lb): A US customary unit that measures either energy/work (force through a distance) or torque (rotational force at a distance from a pivot), depending on context — the two uses share a name and a conversion factor but are physically different quantities.
Newton-Meter (N·m) (N·m): The SI unit of torque, equal to a force of one newton applied at a perpendicular distance of one meter from a pivot point.
Pascal-based pressure units (MPa, bar, kPa) (MPa / bar / kPa): Metric units of pressure built on the pascal (force per square meter). MPa is used for material strength specs, kPa for everyday pressure readings like tire placards, and bar for equipment gauges outside the US.
Horsepower (hp) (hp): A US customary unit of power for engines and motors. This calculator uses mechanical (imperial) horsepower, the standard used for most engine and motor nameplate ratings.

Frequently Asked Questions

Why does amps-to-watts need a voltage input when the other conversions here don't?

Because amps and watts measure two different things. An amp measures how much current is flowing; a watt measures actual power, which depends on both current and voltage (Watts = Amps × Volts). The other six conversions on this tool — ft-lb, N·m, MPa, bar, kW, and psi — are all just two different units measuring the exact same physical quantity, so a single fixed multiplier converts one to the other with no other information needed. Amps and watts aren't the same quantity in different units, so there's no fixed multiplier that works for every circuit — the voltage has to be supplied.

What's the difference between foot-pounds as energy and foot-pounds as torque?

They're two different physical quantities that happen to share both a name and a conversion factor. Foot-pounds of energy (or work) measure a force acting through a distance — the same family as joules. Foot-pounds of torque measure a rotational force applied at a distance from a pivot point — the same family as newton-meters. The numeric conversion factor (1.35582) is identical either way, which is exactly why it's easy to mislabel one as the other. A wrench torque spec and a bullet's muzzle energy might both say "1,000 ft-lb," but they are not the same kind of measurement and shouldn't be compared directly.

How accurate are the conversion factors used here?

The pressure, torque, and power conversions (ft-lb, N·m, MPa, bar, kW, psi, kPa) use the exact factors published in NIST Special Publication 811 (Guide to the SI), rounded to 6 significant figures — the same standard reference used by engineers and machinists. These are exact unit-definition conversions, not estimates, so precision loss only comes from how many decimal places you choose to keep in your own work.

Does the amps-to-watts formula work for AC power with motors or other reactive loads?

Not exactly. Watts = Amps × Volts is accurate for DC circuits and for purely resistive AC loads — space heaters, incandescent bulbs, resistive heating elements. Motors, transformers, and other loads with inductance or capacitance draw current that isn't perfectly in phase with voltage, so their real power is lower than Amps × Volts by a power factor: Watts = Amps × Volts × Power Factor. Treat the plain Amps × Volts result as an upper-bound estimate for reactive loads, not an exact reading, unless you also know the load's power factor.

Why do MPa, bar, and psi all measure the same thing with different numbers?

They're all units of pressure (force per unit area), just built on different base units and used by different industries or regions. Psi (pounds per square inch) is the standard US customary pressure unit. MPa (megapascals) is the SI unit typically used for material strength specs like concrete and steel. Bar is a metric unit close to atmospheric pressure (1 bar ≈ 1 atm) and is common on tire pressure gauges and compressors outside the US. None is more "correct" than the others — which one you'll see depends on the industry, the country, and the equipment's country of origin.