Microwave Wattage Conversion Chart for Cooking Times
Packet instructions and recipes are written for one wattage, but microwaves vary a lot. If yours is more or less powerful than the one on the label, the time needs adjusting, or you end up with cold spots or overcooked food. This chart and a simple formula make it easy to convert any cooking time to your own microwave.
How wattage changes cooking time
Wattage is simply how much cooking power your microwave delivers. A higher-wattage model heats food faster, so it needs less time. A lower-wattage model heats more slowly and needs longer to do the same job. To match a time written for a different microwave, you scale it by the ratio of the two wattages.
For example, if a packet says five minutes at 800W and your microwave is 700W, the new time is 5:00 × (800 ÷ 700), which works out at roughly 5:45. The same formula works for any starting wattage: instructions written for 900W at four minutes become 4:00 × (900 ÷ 700), or about 5:10, in a 700W oven.
The conversion chart
Most UK packaging is written for an 800W microwave. The chart below takes common 800W times and converts them across the wattages you are most likely to own. Find the 800W time on the left, then read across to your wattage.
| Time at 800W | 600W | 700W | 800W | 900W | 1000W | 1100W |
|---|---|---|---|---|---|---|
| 0:30 | 0:40 | 0:35 | 0:30 | 0:30 | 0:25 | 0:25 |
| 1:00 | 1:20 | 1:10 | 1:00 | 0:55 | 0:50 | 0:45 |
| 2:00 | 2:40 | 2:20 | 2:00 | 1:50 | 1:40 | 1:30 |
| 3:00 | 4:00 | 3:30 | 3:00 | 2:40 | 2:25 | 2:15 |
| 4:00 | 5:20 | 4:35 | 4:00 | 3:35 | 3:15 | 2:55 |
| 5:00 | 6:40 | 5:45 | 5:00 | 4:30 | 4:00 | 3:40 |
| 6:00 | 8:00 | 6:55 | 6:00 | 5:20 | 4:50 | 4:25 |
| 8:00 | 10:40 | 9:10 | 8:00 | 7:10 | 6:25 | 5:50 |
| 10:00 | 13:20 | 11:30 | 10:00 | 8:55 | 8:00 | 7:20 |
Times are rounded up to the nearest five seconds. Always check food is piping hot and add short bursts if needed.
Quick multiplier table
If your instructions are written for 800W and you would rather work it out on the fly, multiply the stated time by the figure for your wattage. For a different reference wattage, use the formula above instead.
| Your wattage | Multiply an 800W time by |
|---|---|
| 600W | 1.33 |
| 700W | 1.14 |
| 800W | 1.00 |
| 900W | 0.89 |
| 1000W | 0.80 |
| 1100W | 0.73 |
| 1200W | 0.67 |
How to find your microwave’s wattage
The wattage that matters for cooking is the output power, not the input power. The input figure on the rating plate, often 1200W or more, is the electricity the appliance draws, which is always higher than the cooking output. You are looking for the lower output figure, sometimes labelled as the microwave or cooking power. For more on what the numbers mean, our guide to microwave power ratings breaks it down.
You will usually find the output wattage in one of these places:
- On a label inside the door frame
- On a sticker on the back or base of the appliance
- In the instruction manual or on the original box
No label to hand? You can estimate the output with a quick test. Heat 250ml of cold water on full power and time how long it takes to reach a rolling boil. Around two minutes points to roughly 1000W, about two and a half to three minutes suggests 700W to 800W, and noticeably longer indicates a lower output. It is a rough guide, but enough to pick the right column above.
Keeping food safe
When you convert to a lower wattage, the bigger time is not optional. Leaving the original time unchanged is the most common way to end up with food that is hot at the edges and cold in the middle, which is a food safety risk rather than just a quality one.
The golden rule
The Food Standards Agency is clear that reheating means cooking again, not simply warming through, and that the times printed on packaging may not be enough on their own. Whatever the chart says, the food itself is the real test: it should be steaming hot all the way through, and reheated only once.
A few habits make converted times far more reliable:
- Stir or rotate partway through, as microwaves leave hot and cold spots.
- Cover the food to trap steam and help it heat evenly, using a microwave-safe container.
- Observe any standing time, which lets the temperature even out before you check it.
- Check the centre, not just the edges, and add short bursts if it is not piping hot.
Key takeaways
- To convert a time, multiply it by the stated wattage divided by your microwave’s wattage.
- Lower wattage needs more time, higher wattage needs less.
- Most UK packaging is based on 800W, so use that row of the chart as your starting point.
- Find your output wattage on a label or in the manual, not the higher input figure on the rating plate.
- Always finish by checking the food is steaming hot all the way through, and reheat only once.
Frequently asked questions
Multiply the stated time by the stated wattage divided by your microwave’s wattage. For example, a five minute time written for an 800W oven becomes about 5 minutes 45 seconds in a 700W oven, because 5:00 multiplied by 800 divided by 700 is roughly 5:45. Always check the food is piping hot and add short bursts if needed.
In the UK, packaging is most often based on an 800W or 900W microwave, and many packs list times for both. If your model differs, use the conversion chart or the simple formula to adjust, then check the food is steaming hot throughout.
Not if you adjust the time. A lower-wattage model simply needs longer to deliver the same heat. The risk is leaving the time unchanged, which can leave food undercooked. Always extend the time to match your wattage and make sure the food is piping hot all the way through.
Check the label inside the door frame, on the back of the appliance, or in the manual, and look for the output or cooking power rather than the higher input figure on the rating plate. If you cannot find it, heating a cup of cold water on full power gives a rough guide, with around two minutes to a rolling boil suggesting roughly 1000W.
Round up, especially when converting to a lower wattage. It is safer to start with slightly more time, check the food, and stop early if needed, than to undercook it. Heating in short extra bursts at the end gives you the most control.
Microwaves create hot and cold spots, so heat is rarely perfectly even. Stir or rotate the food partway through, cover it to trap steam, and let it stand for a minute or two after heating so the temperature evens out before you check it.
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