Example 1
P = 460 W.
Power from voltage and current calculator
Type voltage U [V] and current I [A]. The calculator computes circuit power P = U·I. 230 V and 10 A is 2300 W, also shown as 2.3 kW, the order of a heater nameplate.
Voltage from power: U = P/I. Mechanical rate: P = W/t.
Result
Voltage U (V) and Current I (A). The result shows up here.
How it works
Electric power is voltage times current: P = U·I. At 230 V and 10 A you get 2300 W, 2.3 kW on the page. At 12 V and 10 A you get 120 W, not 2300 W: same current, different nameplate voltage. 230 V and 2 A give 460 W. An LED at 5 V and 0.02 A is 0.1 W. A 1.5 V cell at 0.1 A is 0.15 W.
The form has two fields: U in volts, I in amperes. The result is in watts. From 1000 W the calculator also shows kilowatts, so 2300 W does not look like a typo. 12 V and 0.5 A give 6 W. A comma and a period are the same current: 4,5 and 4.5. Convert milliamps: 20 mA is 0.02 A.
Typed 0 V or 0 A gives 0 W: no voltage or no current. A negative U or I is energy direction, not a unit mix-up. Both fields need a number before 2300 W can appear. The 230 and 10 example fills after you click that example button.
U = P/I and I = P/U live on sibling pages. Same triplet, different unknown. Efficiency η = P_out / P_in is next door too: here we do not ask for input and output power, only one product from the nameplate.
P = W/t computes power from joules and seconds, not from volts. 2300 W for an hour is 2.3 kWh of energy, but this calculator stays in watts. Electrical work W = U I t is yet another page: time enters there.
Type 230 and 10, click Calculate, and match 2300 W and 2.3 kW. Then 12 and 10: 120 W. 2300 W at 12 V would need about 192 A, so do not guess the voltage as “like at home”.
How to use
- In the first field enter voltage U in volts. For example 230 at a wall socket or 12 on a car rail. Take the value from the nameplate, not from memory.
- In the second field enter current I in amperes, for example 10. Convert milliamps: 20 mA is 0.02. At 5 V that is 0.1 W, like the LED on the page.
- Click Calculate. The calculator multiplies U by I. 230 V and 10 A give 2300 W, or 2.3 kW. 12 V and 10 A give 120 W. 230 V and 2 A give 460 W.
- Typed 0 V gives 0 W. Both fields need a number. From 1000 W the calculator also shows kilowatts, so a large result stays readable.
- Need U from power? Open U = P/I. Rate from joules is on P = W/t. Efficiency is separate. Here it stays P = U·I.
Formula
P = U · I
Unit: W (1 W = 1 V·A). From 1000 W the calculator also shows kW.
P, U, and I at 230 V and 10 A
Circuit power is the nameplate product. 230 V and 10 A give 2300 W, also shown as 2.3 kW, heater order, not efficiency.
- P
- Power [W]: P = U·I. From 1000 W the calculator also writes kW, so 2300 W does not look like a typo.
- U
- Voltage [V] from the nameplate. 12 V and 10 A is 120 W, not 2300 W: same I, different rail.
- I
- Current [A]. 20 mA is 0.02 A; at 5 V that is 0.1 W, the LED on the page.
Real-life examples
Example 2
P = 6 W.
Example 3
LED: P = 0.1 W.
Example 4
P = 2300 W (2.3 kW).
Example 5
P = 120 W.
Example 6
P = 3.7 W.
Example 7
P = 110 W.
Example 8
P = 960 W.
Example 9
AA battery: P = 0.15 W.
Example 10
P = 6000 W (6 kW).
Ways to use this calculator
- You check heater power from the nameplate U and I.
- You compare 12 V and 230 V at the same current.
Frequently asked questions
How many watts at 230 V and 10 A?
Power is 2300 W, or 2.3 kW. That is the product 230 × 10. At 12 V and the same 10 A you only get 120 W, so take voltage from the nameplate.
Which units do I type?
Voltage U [V], current I [A]. Result P [W], and from 1000 W the calculator also writes kilowatts. Type 20 mA as 0.02 A.
What if 0 V or 0 A?
You get 0 W. No voltage or no current means no power. Both fields need a number before a result appears.
Where do I find U from P and I?
On the voltage-from-power page. Here you solve for P, there for U. Same triple P, U, I, different unknown.
Does this calculator compute efficiency?
No. η = P_out/P_in lives on the efficiency page. Here there is only the product U·I, with no input and output pair.
How is P·t different from P = U·I?
P = U·I is power P [W]. P·t is energy. 2300 W for one hour is 2.3 kWh, and time lives on the electric-work page.
Is 10 A at 12 V also 2300 W?
No. 12 × 10 = 120 W. To get 2300 W at 12 V you need about 192 A, not ten.
Where is P = W/t?
On the power-from-work-and-time page, the one whose H1 is “Power calculator”. Here you stay in the circuit: volts and amperes, no joules.
Does a comma in 4,5 A work?
Yes. 4.5 and 4,5 are the same current. The calculator does not insist on a period.
What about 230 V and 2 A, and 5 V and 0.02 A?
460 W and 0.1 W. The second case is the LED on the page. 12 V and 0.5 A give 6 W.
Knowledge sources
The formula is the school one. Units follow SI; NIST SP 330 and BIPM define the measures, not your result.
Page updated in 2026.