Microwave Wattage Converter

How to use this converter

1. Copy the two numbers off the box. Frozen food almost always prints something like "1100W: 3 min 30 sec". Both halves matter, and most people only read the second one.
2. Put in your own wattage, and make sure it is the right kind. This is where the whole thing goes wrong. The sticker on the back of the cabinet is often the input power, which can be half again as high as the cooking output the package means. The output figure is usually on the label inside the door frame, in the manual, or on the serial plate as "output" or "cooking power". If you cannot find it, switch to the second tab and measure it in a minute with a jug of water.
3. Read the time, then read the power level under it. If your oven is stronger than the package assumes, the better answer is usually the lower power level for roughly the printed time, not full power for less time.
4. Leave the standing time alone. If the box says rest for a minute afterwards, it is still a minute. That step is heat spreading through the food, not the oven adding more.
5. Stop at the check point and look. The card gives you one. Adding thirty seconds is easy; taking thirty seconds back out of an exploded bowl of soup is not.

Why this converter is different

Every page that ranks for this does the same single sum: multiply the time by the package wattage, divide by yours. That sum is correct, and it is also about a third of the problem. The bits nobody handles are the bits that actually ruin dinner.

• It helps you find your real wattage. Every other page says "check the sticker". The sticker very often shows input power, and a converter fed a 1,500 W input figure when the oven cooks at 1,000 W will tell you to undercook everything by a third. The measure tab uses the same water-heating method the manufacturer's own rating comes from.
• It gives you the power level, not just the time. When the package asks for less power than your oven has, matching it on the dial reproduces the gentle heat the instruction assumed. Cooking hotter for less time delivers the same energy and a different result, which anyone who has microwaved cheese sauce at full power already knows.
• It holds standing time out of the conversion. Standing time is thermal, not electrical. Scaling it, as a straight multiply-everything approach invites, makes a five-minute meal a nine-minute one for no reason.
• It says when the swap stops working. Ask most calculators to take a 1,600 W instruction down to a 400 W oven and they will print a number with a straight face. Past a certain gap, cooking four times as long at the same peak power boils the edges before the middle thaws, and the page says so rather than pretending otherwise.
• It prints. There is a sheet behind the PDF button with your pair, a full grid of every common oven wattage, the power-level table, and the water test, sized for the inside of a cupboard door. The one printable chart anyone else offers covers exactly one wattage pair and is a spreadsheet someone dumped into a web page in about 2003.
• The arithmetic is on screen and tested on every build. The result card shows the multiplier and the working. A published 120-row conversion chart, written decades ago and generated independently of this, reproduces row for row here, along with roughly seven thousand further assertions. If any of it drifts, the site does not deploy.

How it works (the math)

There is no lookup table anywhere in this page. A watt is a joule per second, so the energy your food receives is power multiplied by time, and holding that constant gives you the whole thing.

newTime   = boxTime x (boxWatts / yourWatts)
powerLevel = round(levels x boxWatts / yourWatts)
yourWatts  = grams x 4.186 x tempRiseC / seconds

1. The time. Energy delivered is E = P x t. To put the same energy into the food from a different machine you need P1 x t1 = P2 x t2, which rearranges to the first line above. That is dimensional analysis rather than a measurement, which is why it agrees with every conversion chart ever published on the subject instead of competing with them. An 1,100 watt instruction on a 700 watt oven is a multiplier of 1.571, and three minutes becomes four minutes forty-three seconds.

2. The power level. Almost every microwave that is not an inverter model has one magnetron with one output. It does not run at half power; it runs at full power for half the time, switching on and off over a cycle of roughly twenty to thirty seconds. So power level 6 on a 1,100 watt oven averages about 660 watts, which is very nearly the 700 watts a package might be asking for. Matching the level and keeping close to the printed time gives you the heating the recipe was written around. The catch is the cycle length: on a forty-second cook at a low level, the magnetron may be off for most of the time you are standing there. Under a minute, use full power.

3. The wattage measurement. Heating water is calorimetry, and water's specific heat is 4.186 joules per gram per degree Celsius. Warm a known mass by a measured amount over a known time and the power follows. This is exactly the method behind IEC 60705, the standard under which manufacturers declare microwave output power, and behind the IMPI two-litre test, whose industry shorthand is "watts equals seventy times the temperature rise in Celsius". Run the real arithmetic on their two litres and two minutes two seconds and you get 68.6 times the rise, so the famous seventy is our equation rounded off.

Limitation, and it is the honest one. Holding total energy constant is not the same as holding the result constant. A microwave heats water molecules, unevenly, from the outside of the cold spots inwards, and a longer cook at the same peak power gives the edges more time to overshoot while the middle catches up. That is why the card offers a power level, why it hands you a point to stop and stir, and why it flags the gaps that are too wide to bridge with time alone. Treat the number as where to set the keypad, not as a guarantee about the food. USDA wants leftovers, and anything with meat, poultry, egg or seafood in it, at 165 degrees Fahrenheit, and the only way to know is to measure the food.

Three worked examples

A frozen dinner written for 1,100 W, in a 700 W dorm microwave

This is the most searched pair on the subject and the most brutal. The multiplier is 1.571, so a printed three and a half minutes becomes five and a half. What the box will not tell you is that the extra two minutes are not free: the sauce at the edge of the tray is boiling for the whole of them. Cook it in two goes, stir at the check point the card gives you, and the middle arrives warm instead of the corners arriving burnt. If a 700 watt box is the only thing in your kitchen, the honest advice is to stop asking it to cook and let it reheat: our rice cooker guide covers the machine that takes the worst of those jobs off it.

A 1,000 W instruction in a 1,250 W over-the-range oven

Here the arithmetic runs the other way and everything finishes early: four minutes becomes three minutes twelve. The risk flips from undercooking to scorching, and the better answer is on the second line of the card. Power level 8 on a 1,250 watt oven averages 1,000 watts, which is exactly what the package asked for, so you can run the printed four minutes unchanged and get the result the manufacturer tested. This is the single most useful thing on this page and no other converter offers it.

A microwave pasta cooker with no wattage on the label

Plastic microwave cookware tends to ship with times and no wattage at all, or a wattage that turns out to be the input figure. Measure yours: a litre of water, sixty seconds at full power, a thermometer before and after. A rise of twenty-six Fahrenheit is a 1,000 watt oven, eighteen is a 700 watt one. Then convert the box time against whatever the cooker assumes, which for most of them is 1,100 W. The Fasta Pasta cooker we rate for stovetop-free kitchens is exactly this case: it cooks a pound of pasta properly, and every complaint about it being underdone traces back to a microwave weaker than the instructions assume.

Frequently asked questions

How do I convert 1000W to 700W in a microwave?

Multiply the time by 1.43. A 1,000 watt instruction takes about 43 per cent longer in a 700 watt oven, so three minutes becomes four minutes eighteen seconds, and five minutes becomes seven minutes nine. The sum is the package wattage divided by yours, which is 1000 / 700 = 1.4286. Leave the standing time as printed, and stir partway if the food is dense.

How do I convert a 1200-watt microwave to a 1000-watt microwave?

If the instruction is written for 1,200 W and you have 1,000 W, multiply by 1.2. If it is the other way round, a 1,000 W instruction in a 1,200 W oven, multiply by 0.83, or better, set power level 8 and use the printed time unchanged. Level 8 on a 1,200 watt oven averages 960 watts, which is close enough to the instruction that the food behaves the way the manufacturer tested it.

Where do I find my microwave's wattage?

Look for a label inside the door frame, on the back panel, or on the serial plate, and look for the word output or cooking power. The larger number you will often find nearby is input power, which is what the oven draws from the wall, and it runs roughly 40 to 60 per cent above the cooking output. Feeding the input figure into any converter makes your food come out underdone. If neither number is labelled clearly, measure it on the second tab above: a litre of water, a minute at full power, and a thermometer settles it.

Is there a big difference between a 1,000 watt and a 1,200 watt microwave?

About seventeen per cent on the clock, which sounds small and is not nothing: a six-minute instruction finishes a minute earlier. The bigger practical difference is control rather than speed. A stronger oven overshoots faster on small or delicate items, so it needs the power levels more, not less. If you mostly reheat single plates, the 1,000 watt machine is easier to live with.

Can I pop popcorn in a 700-watt microwave?

Yes, and this is the one case where you should ignore the arithmetic on this page. Popcorn bags are printed with a time range and an instruction to listen, because the bag is finished when the pops slow to two seconds apart, not when a timer says so. A 700 watt oven will take roughly half again as long as the bag's upper figure, and the failure mode at low wattage is unpopped kernels rather than burning. Start at the top of the printed range, then stay in the room and listen.

Related tools

• Recipe Converter and Scaler: scale a batch up without scaling the seasoning up with it.
• Rice to Water Ratio Calculator: the water, time and servings for thirteen grains across three machines.
• Printable Kitchen Conversion Chart: build the sheet you need and pin it inside a cupboard door.
• Browse all free kitchen tools by Nora →

What actually helps

A converter fixes the arithmetic. It cannot fix the fact that a microwave is a narrow tool, and the more you have to convert, the more of your cooking is being done by the wrong machine.

• A thermometer, before anything else. It is the only way to measure your oven's real wattage, and the only way to know whether reheated chicken actually reached 165. Nothing else on this list changes as many outcomes for as little money.
• A kettle, if you are under 800 watts. Boiling water is the single worst use of a weak microwave: three minutes for a mug, unevenly, with a superheating risk at the end. Our stainless kettle guide covers the ones with no plastic in the water path.
• A rice cooker, for the grain. Rice wants a long gentle simmer and a rest, and a microwave gives it a violent boil and a bowl to clean. The rice cookers we rate handle the whole cycle unattended.
• An air fryer, for anything that was crisp yesterday. No wattage of microwave will crisp anything, because it heats water and water leaves as steam. That is a physics limit, not a settings problem. See our non-toxic air fryer guide for the models without PTFE in the basket.

Sources & methodology

• USDA FSIS, Microwave Ovens and Food Safety: the 165 °F target for leftovers and for anything containing meat, poultry, egg or seafood, and the reason standing time is part of the cooking rather than an afterthought.
• IEC 60705: the international standard for measuring household microwave performance. The declared output wattage on your oven comes from a water-load test of exactly the shape used on the measure tab.
• Marie T. Smith, Microwave Cooking for One: a published 1,100 W to 700 W conversion chart, 120 rows, generated independently of this page. Used as a cross-check rather than an input. Every row reproduces.
• Water's specific heat capacity, 4.186 J/g·°C, and the IMPI two-litre test shorthand of 70 times the Celsius rise.

Times convert as the package time multiplied by package wattage divided by your wattage, rounded to the nearest second. Power levels assume duty cycling at the oven's full rated output, which is how every non-inverter microwave produces reduced power; the level shown is the closest the keypad can get. The check point is 85 per cent of the converted time, floored to five seconds, and is a convenience rather than a sourced figure. Measured wattage is grams of water times 4.186 times the Celsius rise, divided by seconds. A fixture suite asserts all 120 rows of the published chart, four independently published multipliers, 1,008 conversion round trips, 944 Celsius and Fahrenheit pairs, 180 measurement round trips, 1,568 printed chart cells against the on-screen result, and roughly two thousand further assertions on every build. Reviewed by Nora Whitfield, CIA Culinary Arts, ServSafe Certified. About Nora · Last reviewed September 21, 2026.

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