Microwave Time by Wattage, and the Kitchen Times That Don’t Scale

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Opens on Chapter 10’s example: A package says 3 minutes at 1,100 watts, and Tamsin’s microwave is 800 watts.

1. Microwave

Package time: minutes

and seconds

Package watts

Your watts

2. Boiling on the same burner

It took (minutes)

for (quarts)

Now (quarts)

3. Doubling a bake

Batter (cups)

Pan length (in)

Pan width (in)

Bigger pan: length

width

4. Thickness

New thickness ÷ old

Enter your numbers, then press Work it out.

How it works

Many cooks scale microwave time by the wattages: time × package watts ÷ your watts. It assumes the oven runs at full rated power the whole time, which isn’t quite true, so treat it as a first guess, check, and add short bursts; package directions come first. On one burner, twice the water takes roughly twice as long to boil. Doubling a batter into a second pan of the same size keeps the depth; into one bigger pan, depth = batter ÷ the pan’s area. Heat creeping into food takes about four times as long to go twice as far, which is why cut size matters (a rule of thumb; browning and the oven change real times).

From the book, Chapter 10. 3 minutes at 1,100 W is about 4.125 minutes at 800 W (4 min 7.5 s, 37.5% longer). Soup that boils in 12 minutes takes about 24 minutes doubled. 4 cups of batter sit 0.90 in deep in an 8 × 8; doubled into a 9 × 13, 0.99 in. Twice the thickness, about 4 times the time; half, about 1/4. Every chapter and its calculator →

Amounts can be typed as 3, 0.75, 3/4, 1 1/2 or 1½. They’re worked as exact fractions and written as a cook measures them: cups in quarters or thirds, then tablespoons, then teaspoons to the nearest eighth. Everything stays in your browser: no sign-up, nothing stored or sent.