Find how many amps an appliance draws, how many watts fit in a current, Ohm's law, kVA to kW and three-phase current, with the formula behind every result.
In direct current, power is P = V × I and Ohm's law ties the four quantities together: V = I × R, P = I² × R and P = V² ÷ R. Given any two, algebra gives the other two, which is what the Ohm's law tab does. In alternating current the power factor cosφ enters, the fraction of apparent power S (in VA) that becomes useful work (real power P, in W): P = S × cosφ. In a single-phase system S = V × I, so the current is I = P ÷ (V × cosφ). A 5,500 W shower is a pure resistance (cosφ close to 1): it draws 25 A at 220 V and 43.3 A at 127 V. The power is the same, only the current changes, and it halves when the voltage doubles. In a balanced three-phase system, with the voltage measured LINE-TO-LINE, S = √3 × V × I and P = √3 × V × I × cosφ. The formula follows from P = 3 × V_ln × I × cosφ with V_ln = V ÷ √3, and the line-to-neutral relation (line-to-line = √3 × line-to-neutral) is the same one that turns 127 V into about 220 V and 220 V into about 380 V. For example, 10 kW at 380 V with cosφ 0.92 needs 10,000 ÷ (√3 × 380 × 0.92) = 16.5 A in each phase. In two-phase with neutral (the same load on each phase) the math uses a factor of 2 and the line-to-neutral voltage. Reactive power is Q = S × sinφ, measured in var: it does no work but circulates and occupies conductor capacity. That is why UPS units and transformers are rated in kVA, and the watts they deliver are kVA × 1,000 × cosφ. The appliance powers on this page are typical nameplate values, only to get started. The tool computes the load current and does not pick a breaker or a wire gauge.
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At 220 V, 25 A (5,500 ÷ 220). At 127 V, 43.3 A (5,500 ÷ 127). A heater element is a pure resistance, so the power factor is 1. That figure is the appliance current: it does not say which breaker or wire to use, which is a job for a licensed electrician.
Use the voltage that reaches the appliance: line-to-neutral (120 V) or across two lines (240 V). Line-to-line in a three-phase system, 120 V line-to-neutral becomes about 381.1 V.
Typical nameplate powers, only as a starting point. Every model differs: the label on your appliance rules. Edit the value freely.
I = 5,500 ÷ (220 × 1) = 25 A
Running for 1 hour it uses 5.5 kWh.
| Appliance | W | A @ 120 V | A @ 240 V |
|---|---|---|---|
| 5500 | 45.83 | 22.92 | |
| 7500 | 62.5 | 31.25 | |
| 4500 | 37.5 | 18.75 | |
| 1000 | 8.333 | 4.167 | |
| 1300 | 10.83 | 5.417 | |
| 1900 | 15.83 | 7.917 | |
| 1400 | 11.67 | 5.833 | |
| 1500 | 12.5 | 6.25 | |
| 2000 | 16.67 | 8.333 | |
| 1800 | 15 | 7.5 | |
| 1200 | 10 | 5 | |
| 200 | 1.667 | 0.8333 | |
| 9 | 0.075 | 0.0375 |
Current of each appliance at 120 V and 240 V with cosφ 1 (the field above). Motors and compressors often have cosφ below 1: change the field to see the effect.
Limit of this tool. It shows the current and powers implied by the load you enter. It does not size a breaker or a cable: that depends on installation method, length, circuit grouping and temperature, and belongs to a licensed electrician or engineer following your local code.