Microwave Wattage Time Converter
＋More features: conversion table for 500–1000W and free wattage entry
Conversion table for 500–1000W
From the time and wattage on the package, this builds one table showing the heating time at 500W, 600W, 700W, 800W and 1000W.
Convert with a wattage that is not in the list
For a wattage such as 850W that is not among the options, type any value from 100 to 2000W here (the time is taken from the fields above).
Frozen food and recipes in Japan give heating instructions by wattage, such as “600W for 1 minute 30 seconds”. This tool tells you what to set on your own microwave when its wattage is different — just enter the time and pick the two wattages. Handy when the package assumes 500W or 600W but your microwave is 700W or higher.
How to use
- Enter the heating time and wattage printed on the package (for example, 600W for 1 min 30 s).
- Pick the wattage of your own microwave.
- The converted time, plus a value rounded to 10 seconds, appears below the moment you pick it — no button needed.
How it is calculated
- The energy a microwave puts into food is power (W) × time. To get the same result, the time is adjusted so that this energy stays the same.
- Converted time = time on the package × wattage on the package ÷ your wattage
- Example: 1 min 30 s (90 seconds) at 600W becomes 90 × 600 ÷ 500 = 108 seconds (about 1 min 50 s) at 500W.
- Microwave timers usually move in 10-second steps, so a value rounded up to the nearest 10 seconds is shown as well.
Sources and assumptions
- This is arithmetic based on energy equivalence (power × time held constant).
- Real heating efficiency varies with the model (inverter or not, cavity shape) and with the food, so the result is only a guide.
Assumptions and notes
- Converting between close wattages such as 500W and 600W introduces little error, but a large jump such as 200W (defrost) to 1000W changes the result more easily.
- Drinks and oily foods can boil over suddenly (superheating) if overheated. Set a shorter time and check.
Frequently asked questions
How many seconds at 500W is 1 minute at 600W?
72 seconds (about 1 min 10 s): 60 × 600 ÷ 500 = 72. To match a microwave timer, set 1 min 10 s to 1 min 20 s.
Where can I check the wattage of my microwave?
It is on the label inside the door or on the side, listed in Japan as 高周波出力 (microwave output). If your model only shows “strong / weak” (強・弱), check the manual for the matching wattage. On many models strong is about 500–600W and weak is about 150–200W.
Does changing the wattage change the taste or texture?
Even with the same total energy, a lower wattage over a longer time tends to heat more evenly. Defrosting is best at a low wattage (150–200W). A high wattage for a short time can leave the centre cold, so stirring or turning the food halfway through is the safe approach.