Example 1
What voltage at 60 W and 0.5 A? U = 120 V.
Voltage from Power and Current calculator
Type power P [W] and current I [A]. The calculator computes voltage U = P/I. 60 W at 0.5 A is 120 V. 2300 W at 10 A is 230 V. Zero amperes does not divide.
Power: P = U·I. Current from power: I = P/U.
Result
Power P (W) and Current I (A). The result shows up here.
How it works
Voltage from power and current is U = P/I, because P = U·I. At 60 W and 0.5 A you get 120 V. At 100 W and 2 A you get 50 V. A 2300 W kettle at 10 A is 230 V. 12 W at 1 A is 12 V. This is the P = U I rearrange, not P itself.
The form has two fields: P in watts and I in amperes. The result is in volts. Type 2.3 kW as 2300. A comma and a period mean the same I: 0,5 and 0.5.
I must not be zero, because you do not divide by zero. Typed 0 in I is rejected. Zero watts at nonzero I gives U = 0. Both fields need a number before 120 V appears.
P = U I is on the neighbouring page and computes watts. I = P/U is the sibling rearrange when you know P and U. U = I R is on Ohm's law, not here.
Larger I at the same P gives smaller U: 60 W at 0.5 A is 120 V, the same 60 W at 2 A is 30 V. The calculator does not check insulation.
Type 60 and 0.5, click Calculate, and check 120 V. Then 2300 and 10: 230 V. The calculator divides P by I; it does not guess the mains.
How to use
- In the first field enter P in watts, for example 60. 2.3 kW is 2300 W.
- In the second field enter I in amperes, for example 0.5 or 10.
- Click Calculate. 60 W and 0.5 A give 120 V, because P = U I. 2300 W and 10 A give 230 V.
- I = 0 is rejected. Zero in P at nonzero I gives U = 0. Both fields need a number.
- For P = U·I, open circuit power. Need I? Open I = P/U.
Formula
U = P / I
I ≠ 0.
U from power and current
The pair of I = P/U: here U = P/I. 60 W and 0.5 A is 120 V. 2300 W and 10 A is 230 V. I cannot be zero.
- U
- The unknown voltage [V]. 60 / 0.5 = 120 V. Not potential V = W/q.
- P
- Power [W]. 2300 W at 10 A is a 230 V mains load.
- I
- Current [A]. I = 0 does not divide. 0.5 A at 60 W.
Real-life examples
Example 2
What voltage at 100 W and 2 A? U = 50 V.
Example 3
What voltage for a 2300 W kettle at 10 A? U = 230 V.
Example 4
What USB voltage at 6 W and 0.5 A? U = 12 V.
Example 5
What LED voltage at 0.1 W and 0.02 A? U = 5 V.
Example 6
What voltage at 500 W and 5 A? U = 100 V.
Example 7
What 12 V system voltage at 120 W and 10 A? U = 12 V.
Example 8
What voltage at 1000 W and 4 A? U = 250 V.
Example 9
What cell voltage at 3.7 W and 1 A? U = 3.7 V.
Example 10
What 48 V rail voltage at 960 W and 20 A? U = 48 V.
Ways to use this calculator
- You check 120 V from 60 W and 0.5 A.
- A 2300 W kettle at 10 A: 230 V.
Frequently asked questions
What is U at 60 W and 0.5 A?
Voltage is 120 V. From P = U·I you divide 60 W by 0.5 A and the supply volts remain.
What about 2300 W and 10 A?
You get 230 V. That is the heater nameplate: 2300 W at ten amperes.
Which units do I type?
Power P [W], current I [A]. Result U [V]. Type 2.3 kW as 2300 W.
How is this different from P = U I?
Here you solve U = P/I. There you compute power from voltage and current. Same triple, different unknown.
Where is I = P/U?
On the current-from-power-and-voltage page. Here the unknown is U, there it is I.
Does a comma in 0,5 work?
Yes. 0.5 and 0,5 are the same current I [A]. A comma and a period mean the same value.
Do I type 2.3 kW as 2.3?
No. Field P wants P [W]. 2.3 kW is 2300 W, otherwise the voltage comes out a thousand times too small.
Where is U = I R?
On the Ohm’s-law page. Here U comes from power and current, not from ohms.
What if I = 0?
The calculator refuses zero amperes. U = P/I at zero current does not exist.
What about 100 W and 2 A?
Voltage is 50 V. A hundred watts on two amperes is half of a typical 100 W at 1 A.
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.