Microwave Wattage Conversion Chart for Cooking Times
Ever followed the timing on a packet to the second and still ended up with a meal that is scalding at the edges and frozen in the middle? The usual culprit is wattage. Packaging is written for one power level, and if your microwave is weaker or stronger the time needs adjusting. Here is the simple formula, a full conversion chart, and how to find your own microwave’s wattage.
Cooking time depends on power: the lower the wattage, the longer the time. To convert, multiply the stated time by the stated wattage divided by your wattage. A lower-powered microwave needs more time, a higher-powered one needs less.
The simple wattage conversion formula
Microwave cooking time is inversely proportional to power. Double the power and you roughly halve the time; halve the power and the time roughly doubles. One small sum handles any conversion:
So if a packet says 5 minutes at 1000W and your microwave is 800W, the sum is 5 minutes times (1000 divided by 800), which is 6 minutes 15 seconds. The chart below in the diagram shows how the same dish stretches out as power drops.
Microwave wattage conversion chart
Find the wattage your instructions were written for on the left, then read across to your own microwave’s wattage. Multiply the stated time by the number in that cell.
| Instructions for | 600W | 700W | 800W | 900W | 1000W | 1100W |
|---|---|---|---|---|---|---|
| 700W | 1.17 | 1.00 | 0.88 | 0.78 | 0.70 | 0.64 |
| 800W | 1.33 | 1.14 | 1.00 | 0.89 | 0.80 | 0.73 |
| 900W | 1.50 | 1.29 | 1.13 | 1.00 | 0.90 | 0.82 |
| 1000W | 1.67 | 1.43 | 1.25 | 1.11 | 1.00 | 0.91 |
Anything above 1.00 means cook for longer, anything below means cook for less. Whichever way you convert, check the food is piping hot before serving and add time in short bursts if needed.
Try the calculator
Start at the shorter time, check the food is piping hot, and add short bursts if needed.
Worked example: converting a real cooking time
Say a soup is labelled 3 minutes 30 seconds at 900W, but your microwave is 700W. Look up the 900W row and the 700W column in the chart, which gives 1.29. Multiply: 3 minutes 30 seconds is 210 seconds, and 210 times 1.29 is about 271 seconds, or 4 minutes 30 seconds. Stir halfway through and check it is hot right to the centre.
How to find your microwave’s wattage
- Check the label. The output wattage is usually printed on a sticker inside the door frame, on the back, or on the serial-number plate. Look for a figure like 800W paired with a category letter.
- Check the manual or the maker’s website. Search the model number to confirm the output power, not the input power, which is a higher number.
- Try the water test. If all else fails, heat 250ml of cold water on full power and time how long it takes to boil. Around 1.5 minutes suggests a higher-powered machine, while 3 minutes or more points to a lower one.
If you are shopping for a new one and want to match modern recipes, our guide to what microwave power rating you need walks through the options.
What do the category letters A to E mean?
Alongside the wattage, UK microwaves and food packaging carry a heating category letter. The scale runs from A, the least powerful, to E, the most powerful, and it exists so packaging can quote different times for different machines. It was developed by the former Ministry of Agriculture, Fisheries and Food with oven and food manufacturers. According to the Microwave Technologies Association, the symbol on the front of the oven gives its maximum power output and the category letter for heating small quantities of food.
| Heating category | Approximate output power |
|---|---|
| A | Up to about 500W (least powerful, now rare) |
| B | About 600W |
| C | About 700W |
| D | About 750 to 800W |
| E | About 800 to 900W (most common) |
The catch is that the letter alone is only a rough guide, and many modern microwaves are more powerful than the bands the system was built around. That is why a machine can be labelled something like 900W Category D. The reliable approach is always to use the actual wattage printed alongside the letter, then apply the chart above.
Reheating safely at any wattage
Getting the time right is about safety as well as taste. A few habits keep every reheat safe:
- Heat until piping hot throughout. The food should be steaming hot all the way to the centre, not just around the edges.
- Stir or turn halfway. Microwaves can leave cold spots, so stirring evens out the heat and removes them.
- Respect the standing time. Food keeps cooking after the microwave stops, so let it stand for the time the packaging suggests.
- Only reheat once. Reheating the same food repeatedly increases the risk of stomach upsets.
Key takeaways
- Cooking time is inversely proportional to wattage: less power means more time.
- To convert, multiply the stated time by the stated wattage divided by your wattage.
- Use the conversion chart to find the multiplier for your machine in seconds.
- Category letters run A (weakest) to E (strongest), but always go by the actual wattage.
- Whatever the maths says, check food is piping hot throughout and stir halfway.
Frequently asked questions
Multiply the stated time by the stated wattage divided by your wattage. For example, 4 minutes at 800W in a 1000W microwave is 4 times 0.8, which is 3 minutes 12 seconds.
Yes. A lower-powered microwave puts less energy into the food each second, so it needs more time to reach the same result.
Most UK packaging quotes times for around 800W to 900W, often alongside a category E rating. Packs usually list a couple of wattages so you can pick the closest.
It rates heating power from A, the least powerful at up to about 500W, to E, the most powerful at about 800 to 900W and the most common. The figures are approximate, so use the actual wattage where you can.
Look for the output wattage on the label inside the door or on the back, or check the manual. If it is missing, time how long it takes to boil 250ml of water as a rough guide.
Higher wattage cooks faster and more evenly, which suits busy households. Lower wattage is fine for reheating and small portions but takes longer.
Want a microwave with the power and preset programmes to take the guesswork out of timings? Explore the CATA range.
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