Amperage & Wattage Calculator
Calculate watts, amps, or volts for DC, single-phase AC, and three-phase AC systems.
How this amperage wattage calculator works
This tool is designed to quickly convert between amperage (A), wattage (W), and voltage (V). In most electrical tasks—whether sizing a power supply, estimating appliance load, or checking a circuit—you typically know two values and need the third. That is exactly what this calculator does.
You can use it for:
- DC circuits (batteries, automotive, solar DC loads)
- Single-phase AC circuits (most homes and small businesses)
- Three-phase AC circuits (industrial motors, commercial equipment)
Electrical basics: amps, watts, and volts
Voltage (V)
Voltage is the electrical pressure pushing charge through a circuit. Common examples are 12V (automotive), 120V (US household), and 230V (many international household systems).
Current / Amperage (A)
Current is the flow rate of electric charge. Higher current usually means thicker wires, larger breakers, and more heat potential.
Power / Wattage (W)
Wattage is the total electrical power being consumed or delivered. If you are trying to estimate energy use, wattage is usually your starting point.
Formulas used by the calculator
DC circuits
P = V × I
- I = P / V
- V = P / I
Single-phase AC circuits
P = V × I × PF
- I = P / (V × PF)
- V = P / (I × PF)
Three-phase AC circuits
P = √3 × V × I × PF
- I = P / (√3 × V × PF)
- V = P / (√3 × I × PF)
Why power factor matters
In AC systems, power factor (PF) accounts for phase difference between voltage and current. A PF of 1 means ideal efficiency; lower PF means more current is needed for the same real power. Resistive loads like heaters are often near 1. Motors and some electronics can be lower, such as 0.8–0.95.
Practical examples
Example 1: Find watts from amps and volts (DC)
If a 12V DC device draws 8A, then power is:
P = 12 × 8 = 96W
Example 2: Find amps from watts and volts (single-phase AC)
A 1500W heater at 120V with PF 1:
I = 1500 / (120 × 1) = 12.5A
Example 3: Find amps in a three-phase system
For 10,000W at 400V with PF 0.9:
I = 10000 / (√3 × 400 × 0.9) ≈ 16.0A
Common use cases
- Checking whether a branch circuit is likely overloaded
- Estimating generator or inverter requirements
- Sizing DC wiring for off-grid and vehicle systems
- Understanding appliance labels and nameplate ratings
- Comparing expected vs measured current draw
Safety reminders
This calculator is for estimation and planning. Real-world installations must follow local electrical codes, conductor ampacity tables, derating rules, temperature limits, and protection device requirements. Always consult a licensed electrician for installation decisions.
- Never exceed breaker or conductor ratings.
- Use appropriate wire gauge for current and distance.
- De-energize circuits before inspection or maintenance.
- Account for surge current on motors and compressors.
FAQ
Can I use this for both residential and industrial systems?
Yes. Choose the correct circuit type (DC, single-phase AC, or three-phase AC) and enter realistic values.
What if I do not know the power factor?
Use the equipment datasheet if possible. If unknown, 0.9 is a common planning value for many AC loads, but actual equipment may differ.
Does higher voltage reduce current for the same watts?
Generally yes. For a fixed power demand, increasing voltage reduces current, which can reduce conductor size requirements and I²R losses.