What this calculator does
A microwave converter solves a problem that trips up most home cooks at least once: a packet, recipe or cookbook states a cooking time for a specific microwave wattage, and the microwave on the bench is a different wattage entirely. Microwaves cook faster as wattage rises and slower as it falls, so using the printed time unchanged either undercooks or overcooks the food.
The relationship is a simple inverse one: double the wattage and the same food needs roughly half the time; halve the wattage and it needs roughly double. This microwave calculator applies that ratio directly, taking the original time and the two wattages involved and returning the adjusted time in minutes and seconds.
The formula
The stated time is multiplied by the ratio of the original wattage to the new wattage. A higher new wattage than the original shrinks the time, and a lower new wattage stretches it, because power and time trade off inversely for a given amount of energy delivered to the food.
| Term | Meaning |
|---|---|
| Original wattage | The microwave wattage the stated cooking time was written for. |
| New wattage | The wattage of the microwave actually being used to cook the food. |
| Power ratio | Original wattage divided by new wattage; above 1 means the new microwave is weaker and needs longer. |
The inputs explained
| Field | What to enter |
|---|---|
| Original cooking time (min) | The cooking time as printed on the packet or recipe. |
| Original microwave wattage (W) | The wattage that time was written for, usually printed alongside it. |
| Your microwave wattage (W) | The wattage of the microwave you are actually cooking in, usually on a sticker inside the door or in the manual. |
When to use it
Cooking packet food on an unfamiliar microwave
Ready meals and popcorn packets are labelled for a specific wattage, commonly 800W or 1000W. A microwave converter turns that label into a workable time for whatever microwave is actually being used, at home, in a share house or on holiday.
Following a recipe written for a different kitchen
Recipes that specify microwave steps assume a wattage the author tested with, which frequently does not match the reader own appliance. Adjusting the stated time avoids a guessing game with the reheat or defrost button.
Replacing an old microwave with a new one
A new microwave is often a different wattage to the one it replaced, so cooking times built up from experience with the old machine need re-scaling rather than reusing as-is.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How a 5-minute, 1000W instruction converts to other microwaves
The same 5-minute instruction, adjusted for a range of common household microwave wattages.
| Your microwave wattage | Adjusted cooking time | Power ratio |
|---|---|---|
| 600W | 8 min 20 s | 1.67× |
| 700W | 7 min 9 s | 1.43× |
| 800W | 6 min 15 s | 1.25× |
| 900W | 5 min 33 s | 1.11× |
| 1000W | 5 min 0 s | 1.00× |
| 1200W | 4 min 10 s | 0.83× |
How the adjusted time scales with the original time, on a fixed 800W to 700W conversion
A range of original cooking times, all converted from an 800W recipe to a 700W microwave.
| Original time (800W) | Adjusted cooking time | Power ratio |
|---|---|---|
| 1 min | 1 min 9 s | 1.14× |
| 2 min | 2 min 17 s | 1.14× |
| 3 min | 3 min 26 s | 1.14× |
| 5 min | 5 min 43 s | 1.14× |
| 10 min | 11 min 26 s | 1.14× |
| 15 min | 17 min 9 s | 1.14× |
Questions
Where do I find my microwave wattage?
It is usually printed on a sticker inside the door frame, on the back panel, or listed in the instruction manual or manufacturer website using the model number. It is stated in watts (W), commonly somewhere between 600W and 1200W for a household microwave.
Is the conversion exact?
It is a close and widely used approximation, not a lab-precise figure. Real microwaves vary in cavity size, turntable speed and how evenly they distribute energy, so it is still worth checking the food partway through, especially the first time you cook something on a newly converted time.
Does this work for defrosting as well as cooking?
The same inverse relationship applies, though most microwaves run defrost cycles at a reduced, pulsed power rather than full wattage, so treat a converted defrost time as a starting point and check the food is defrosting evenly rather than relying on the time alone.
What if my new wattage is much higher than the original recipe?
The calculated time will be noticeably shorter, and it is worth checking the food earlier than that shorter time to avoid overcooking, since a big jump in wattage can also change texture, not just cooking speed.
For converting other everyday kitchen quantities, see the fuel consumption calculator for a different kind of everyday conversion, or browse the full calculator list for more.