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Amps Calculator

Electrical current in amps is calculated using the formula I = P / V, where P is power in watts and V is voltage in volts. A 1,500-watt heater plugged into a standard 120-volt outlet draws 12.5 amps. This calculator provides three conversions: find amps from watts and volts, find watts from amps and volts, or find volts from amps and watts. Enter any two known values to calculate the third.

Quick Answer

A 1,500-watt appliance on a 120-volt circuit draws 12.50 amps.

Find Amps (I = W / V)

Find Watts (P = A x V)

Find Volts (V = W / A)

Common Examples

Input Result
1,500W at 120V 12.50 amps
2,400W at 240V 10.00 amps
15A at 120V 1,800 watts
20A at 240V 4,800 watts
1,800W at 15A 120.00 volts

How It Works

The Formulas

These three conversions are all derived from the basic electrical power equation:

P = I x V (Power equals Current times Voltage)

Rearranged to solve for each variable:

  • Amps (I) = Watts (P) / Volts (V)
  • Watts (P) = Amps (I) x Volts (V)
  • Volts (V) = Watts (P) / Amps (I)

Where:

  • I = current in amperes (amps)
  • P = power in watts
  • V = voltage in volts

Understanding Amps, Watts, and Volts

Amps measure the flow of electrical current, similar to the volume of water flowing through a pipe. Volts measure the electrical pressure or force pushing the current, like water pressure. Watts measure the total power being consumed or delivered, combining both flow and pressure.

Common Household Voltages

In North America, standard household outlets provide 120 volts. Large appliances (electric dryers, ovens, central AC, water heaters) use 240-volt circuits. These higher-voltage circuits deliver more power at the same amperage, which is why they are used for high-demand appliances.

Circuit Breaker Ratings

Standard residential circuits are protected by breakers rated at 15 or 20 amps for 120-volt circuits and 30, 40, or 50 amps for 240-volt circuits. The National Electrical Code recommends loading a circuit to no more than 80% of its breaker rating for continuous loads. A 15-amp circuit should carry no more than 12 amps of continuous load, and a 20-amp circuit no more than 16 amps.

Appliance Amperage Examples

  • LED light bulb (10W at 120V): 0.08 amps
  • Laptop charger (65W at 120V): 0.54 amps
  • Microwave (1,000W at 120V): 8.33 amps
  • Space heater (1,500W at 120V): 12.5 amps
  • Electric dryer (5,400W at 240V): 22.5 amps
  • Central AC (3,600W at 240V): 15 amps

Worked Example

A 1,500-watt space heater plugged into a 120-volt outlet: Amps = 1,500 / 120 = 12.5 amps. This is within the capacity of a 15-amp breaker at 83% load, but above the 80% continuous load recommendation (12 amps). Running this heater along with other devices on the same circuit may trip the breaker. On a 20-amp circuit, 12.5 amps is 62.5% of capacity, well within safe limits.

For a 240-volt electric dryer rated at 30 amps: Watts = 30 x 240 = 7,200 watts. This is why dryers require dedicated 30-amp, 240-volt circuits.

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Frequently Asked Questions

How many amps does a typical household outlet provide?
Standard household outlets in the United States are on either 15-amp or 20-amp circuits at 120 volts. A 15-amp circuit can safely deliver a continuous load of 12 amps (80% of the breaker rating), which equals 1,440 watts. A 20-amp circuit can continuously deliver 16 amps, or 1,920 watts. The outlet itself may be rated for 15 or 20 amps.
What is the difference between amps and watts?
Amps measure the amount of electrical current flowing through a circuit, while watts measure the total power consumed. The relationship is Watts = Amps x Volts. A device can draw few amps but high watts if the voltage is high (like a 240V dryer), or many amps at low watts if the voltage is low. Watts is the more useful measure for calculating energy cost, while amps determines the required circuit and wire size.
Why do some appliances use 240 volts instead of 120 volts?
High-power appliances like electric dryers, ovens, and water heaters use 240 volts because it allows them to deliver more power while drawing fewer amps. A 5,400-watt dryer at 240V draws only 22.5 amps, while the same wattage at 120V would require 45 amps, needing much thicker (and more expensive) wiring. Higher voltage is more efficient for high-power loads.
Can I run two high-wattage devices on the same circuit?
It depends on the circuit capacity. Add the amperage of both devices and compare to the circuit breaker rating (at 80% for continuous loads). Two 1,500-watt heaters on a 120V, 15-amp circuit would draw 25 amps total (12.5 each), far exceeding the 15-amp breaker. Each heater needs its own circuit, or one can be moved to a different circuit.
Does this formula work for DC (direct current) circuits?
Yes, the formula P = I x V applies directly to DC circuits. For single-phase AC circuits (standard household), it provides a close approximation assuming a unity power factor. For motors and inductive loads on AC circuits, the actual current may be higher than P / V due to a power factor less than 1. This calculator assumes resistive loads with a power factor of 1.