Volts to Watts
With voltage 12 V, amps, ohms or watts 5, volts to watts comes to 60.00 W — watts. It is reached in 4 steps, the last of which is 12 * 5, and each one is printed on the page with its numbers filled in. The formula is the one published by NIST SP 811, not an approximation fitted to it.
Volts alone do not give watts — one more quantity is required. Enter amps, ohms or the wattage and this gives the rest of the set.
Formula and sources checked · How we check
Voltage 12 V, And I also know the Current, in amps, Amps, ohms or watts 5
60.00 W
Watts for the example below. Editing a field recomputes the calculator below; this figure holds the answer the page was loaded with.
It is written into the HTML rather than drawn by a script, so a search engine reading this page without running JavaScript still finds an answer.
- Current
1 * 5 + 0 * (12 / 5) + 0 * (5 / 12)5 A- Power
12 * 560 W- Resistance
12 / 52.4 ohm- Energy if it ran all day
60 * 24 / 10001.44 kWh
Worked example
12 V at 5 A is 60 W. The same 12 V through a 5 ohm resistor is 2.4 A and 28.8 W — the same two numbers in a different role give an answer less than half as large, which is why "volts to watts" cannot be answered without saying which.
How to work it out yourself
- 1.Say what the second quantity is. Volts alone describe a pressure, not a flow, so no wattage exists until something is drawing current.
- 2.For a power supply or battery, the amps are on the label — a 12 V 2 A adapter is 24 W.
- 3.For a heating element or a resistor, use ohms. The current is volts ÷ ohms, and the power is volts² ÷ ohms.
- 4.Choosing watts as the second figure runs it the other way: 60 W at 12 V is 5 A, which is the number that decides the fuse.
Volts to watts at 5 amps
| Voltage (V) | Watts | Resistance |
|---|---|---|
| 3.3 | 16.50 W | 0.66 ohm |
| 5 | 25.00 W | 1 ohm |
| 9 | 45.00 W | 1.8 ohm |
| 12 | 60.00 W | 2.4 ohm |
| 24 | 120.00 W | 4.8 ohm |
| 48 | 240.00 W | 9.6 ohm |
| 110 | 550.00 W | 22 ohm |
| 120 | 600.00 W | 24 ohm |
| 220 | 1,100.00 W | 44 ohm |
| 230 | 1,150.00 W | 46 ohm |
| 240 | 1,200.00 W | 48 ohm |
| 277 | 1,385.00 W | 55.4 ohm |
The rail voltages of everything from a microcontroller to a commercial lighting circuit, at a fixed 5 A. Watts rise in step with volts because current is being held constant here — in a real circuit a higher voltage usually means less current for the same power.
The formula
- Current
1 * 5 + 0 * (12 / 5) + 0 * (5 / 12) - Power
12 * 5 - Resistance
12 / 5 - Energy if it ran all day
60 * 24 / 1000
Source: NIST SP 811 — the SI units volt, ampere, ohm and watt, BIPM SI Brochure, 9th edition — derived units
Questions people actually ask
- How many watts is 12 volts?
- Any number at all, until the current is known. 12 V at 1 A is 12 W; 12 V at 20 A is 240 W. Volts measure pressure and watts measure rate of energy transfer, so one cannot become the other without the flow between them.
- How do you convert volts to watts?
- Multiply by the current: watts = volts × amps. With resistance instead of current, watts = volts² ÷ ohms. On AC add the power factor: watts = volts × amps × PF.
- How do you convert watts to volts?
- Divide by the current: volts = watts ÷ amps. A 60 W load drawing 5 A is on a 12 V supply. This one is asked less often than it should be, because a supply voltage is normally fixed and it is the current that varies.
- How do you get amps from volts?
- With the resistance: amps = volts ÷ ohms, which is Ohm's law. With the power: amps = watts ÷ volts. A 1,200 W hair dryer on 120 V draws 10 A.
- Does this apply to AC?
- The volts-to-amps part does, using RMS values, which is what a household voltage is quoted in. The watts part needs the power factor for anything with a motor or a transformer: at 0.8 PF, 120 V and 10 A is 960 W rather than 1,200.
Related
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