Amp Calculator

The Power Triangle: Understanding Amperage

Electricity drives the modern world, but it can be confusing. You buy a 1000W microwave, plug it into a 120V outlet, and hope it doesn't trip the 15A breaker. How do these numbers relate? Our Amp Calculator uses the fundamental laws of electricity (Ohm's Law and the Power Watt Law) to keep your circuits safe.

The Formulas

For DC circuits (and simplified AC resistive loads), the relationship is straightforward:
$$Power (Watts) = Voltage (Volts) \times Current (Amps)$$
$$P = V \times I$$

To find Amps:
$$I = P / V$$
Example: A 1200 Watt heater on a 120 Volt circuit.
$1200 / 120 = 10$ Amps.

To find Watts:
$$P = V \times I$$
Example: A car amplifier draws 30 Amps at 12 Volts.
$12 \times 30 = 360$ Watts.

AC vs. DC

The formulas above work perfectly for DC (Direct Current, like batteries) and AC resistive loads (like heaters and incandescent bulbs).
However, for inductive loads (motors, compressors, refrigerators), you must account for the Power Factor (PF).
$$Amps = Watts / (Volts \times PF)$$
A motor might use more amps than the raw wattage suggests because the current and voltage are out of phase. For home safety calculations, it is safer to overestimate amperage, so using the simple DC formula provides a built-in safety margin.

Circuit Breaker Safety

Household circuits are typically rated for 15 Amps or 20 Amps.
The 80% Rule: For continuous loads (running 3+ hours), you should not exceed 80% of the breaker's capacity.
- 15 Amp Breaker: Max continuous load = 12 Amps (1440 Watts).
- 20 Amp Breaker: Max continuous load = 16 Amps (1920 Watts).
This is why plugging two space heaters into the same outlet almost always blows a fuse.

Wire Gauge

Amperage determines wire thickness. Pushing too many amps through a thin wire causes it to melt and catch fire.
- 14 AWG wire = Max 15 Amps.
- 12 AWG wire = Max 20 Amps.
- 10 AWG wire = Max 30 Amps.
Never replace a breaker with a larger one without upgrading the wire first!