How long in the microwave at a different wattage?
The label says 5:00 at 1000W, but your oven is 800W? The label time does not carry over — it must be recalculated for the energy the food needs.
On the label: 5:00 at 1000W. Your oven: 800W. → Set about 6:15.
Calculator
or type another power, between 100 and 3000 W
write 5:00, 5 or 1.5 (minutes); 90s means 90 seconds
= 300 seconds
the power is printed on the door or manual, between 100 and 3000 W
Set your oven to
6:15
exact: 6:15
power -20% → time +25%
6:15
What it usually comes to
Times written for 1000W, converted for the most common ovens. All are rounded to 5 seconds, the way ovens are actually set.
| On the label (1000W) | At 700W | At 800W | At 900W |
|---|---|---|---|
| 1:00 | 1:25 | 1:15 | 1:05 |
| 2:00 | 2:50 | 2:30 | 2:15 |
| 3:00 | 4:15 | 3:45 | 3:20 |
| 5:00 | 7:10 | 6:15 | 5:35 |
| 8:00 | 11:25 | 10:00 | 8:55 |
Why it comes out this way
Food needs the same energy whatever the oven, and energy is power multiplied by time. When power drops, time rises so the product stays the same:
new time = old time × old power / new power
That also explains the surprise: when power drops 20%, from 1000W to 800W, time does not rise 20% but 25% — because you divide by a smaller number. The result is rounded to 5 seconds, the step ovens use in practice.
It is a good approximation, not a guarantee: ovens differ, and food heats unevenly. Stir or turn halfway, respect the standing time on the label, and check the food is hot throughout before eating.
Frequently asked questions
My oven is 700W and the label says 900W. What do I multiply by?
By 900 divided by 700, about 1.29: the time grows by roughly 29%. For example, 3:00 at 900W becomes about 3:50 at 700W.
Why does the time grow more than the power shrinks?
Because the time is divided by the new, smaller power. When power drops 20% (from 1000W to 800W), time rises 25%: 5:00 becomes 6:15.
Does the conversion work for defrosting?
Not really. Defrosting uses special low-power cycles and the time depends on weight. Use your oven's defrost programme.
How do I convert for a power level like P80?
Multiply the oven power by the level: P80 on an 800W oven means about 640W effective. Enter 640W as your oven power and check the food at the end.
Why is my food hot at the edges and cold in the middle?
Microwaves heat unevenly. Stir or turn the food halfway, let it stand a minute or two after, and check it is hot throughout. The converter adjusts the time, not the evenness.
Sources and method
- The old-time × old-power / new-power formula is the standard method of dedicated converters, for example the OmniCalculator converter.
- For microwave food safety — standing times, stirring, temperatures — see the USDA “Microwave Ovens and Food Safety” fact sheet.
- Every figure on the page — the example, the table and the answers — uses the same formula, rounded to 5 seconds.