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Tool

Headlight wattage

The estimate is P = V × I, the inverse of the current calculator. Voltage is a field. The default is 13.5 V. Current is in amperes. The figure is electrical arithmetic from your numbers. It is not a bulb catalog and not a legal wattage limit.

Tap Example to fill 13.5 V and 4.1 A, a clamp-meter reading on one low beam. Then type the amperes you actually measured.

13.5 V is the running default. You can set 12 V.

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Enter volts and amperes. The estimate will name watts in a full sentence.

This figure is an educational estimate. It is not a product listing, not DOT or SAE certification, and not legal advice on aftermarket lamps. Aiming and wattage do not make a lamp street-legal. Check the vehicle manual and local law.

When this estimate fits

Worked numbers from this formula

13.5 V × 4.07 A is about 55 W. Does that match the stamp on the bulb?

12 V × 4.58 A is also about 55 W. Same watts, different voltage, different current.

13.5 V × 20 A is 270 W. That is a large lighting load. The page still multiplies the two fields and does not call the result street-legal.

Questions

Is this the wattage printed on the bulb?

Only if your volts and amperes describe that bulb. The estimate multiplies the two fields. It does not read a catalog.

Why default to 13.5 V?

That is a typical running voltage with the alternator online. The current page uses the same default, so the two tools stay inverse.

Can watts tell me if a lamp is legal?

No. Wattage does not make a lamp street-legal. Check the vehicle manual and local law.

Compare two wattage sets if you have halogen and LED numbers.