# Energy efficiency of microwave and electric kettle for heating water

Has anyone measured the watts used to heat a mug of water in a microwave instead of in electric kettle into cold mug? I have always considered that an electric kettle wastes energy when heating enough water for a mug of coffee or tea. Enough water must be added to cover heating element and often surplus is left with hot element.Instead I have an old tupperware mug with two finger handle for safe use. The correct amount of water is added. The heating is watched until it boils and then used immediately door opened.

• I'm voting to close this question as off-topic because it doesn't seem like a culinary question but rather how electrical appliances work
– Divi
Mar 4, 2020 at 21:15
• Partial answer: your microwave probably has an input power rating as well as a thermal output power rating. That should give you a good indication of an upper bound of your microwave efficiency. Mar 5, 2020 at 19:24

According to the folks over at treehugger.com, they did a study to measure which of the stove, the microwave or the kettle was the more efficient in terms of use of electricity to heat a standard mug of water. This doesn't directly answer your question as you are unlikely to boil 350 ml (standard cup is 250 ml) of water in your kettle or on the stove, but it gets the point across.

A summary of their findings is that it took the electric stove 0.11 kWh, the microwave (900 W) 0.07 kWh, and the kettle 0.04 kWh. This indicates that in terms of energy usage the stove is 30.5% efficient, the microwave is 47% and the kettle is 81%.

The clear winner is the kettle!

• Ach, I always forget that in the US, with only 110v, a kettle takes half a lifetime to boil. No-one in the EU has had a stove-top kettle in decades. I think they went out of fashion in the 1960's. My answer is based on an electric kettle only, but is voltage-independant. The math works with 220 or 110v. Mar 4, 2020 at 9:50
• I had a syove top kettle in tge 80s, in Britain (which was in the EU at the time). I think tgey continue to be popular with people who have ‘always on’ stoves such as Agas and Raeburns. Mar 4, 2020 at 10:24
• @Tetsujin Heathen ikea.com/de/de/p/metallisk-wasserkessel-edelstahl-40360222 Mar 4, 2020 at 10:27
• @SZCZERZOKŁY - yup, looks like one for the Aga, gin & Jag community ;) Mar 4, 2020 at 10:29
• Out of curiosity, this means that boiling 75cl in a kettle (usually, that is the minimum amount you need in order for not to break the kettle), is even more efficient, right? It can heat up 3 cups for 0.04kWh whereas the rest should be multiplied by 3 for 75cl?
– M.K
Mar 4, 2020 at 10:31

Have you considered a kettle with an embedded element? I don't think I've seen a 'floating' element kettle in 20 years. Jug kettles [tall & thin] are capable of boiling half a cup of water in about 30 seconds.

You can do the math [approximately] yourself on the equipment you currently have.

Assume a kettle is 2kW a microwave 1kW

As you can't put one cupful in your kettle, you'll have to work with what you can.
Put minimal water in kettle, boil & time it.
Put one cup in the microwave, boil & time it.

If the microwave takes more than twice the time of the kettle, the kettle is more efficient.

This would be more accurate once you know the precise wattage of both devices & far more energy-efficient with a modern jug kettle.

Note the amount of heat energy getting into the water is not necessarily the entire output of the heating device, so timing it & multiplying by the wattage is the only simple & effective way to tell how much energy was used.

Also note that convection is less effective in a microwave, so you will have to stir half-way. Water can boil at the top yet still only be 50° at the bottom of a cup.

• Also if you put CUP of water in microwave there might be more CUP than water in there. Mar 4, 2020 at 10:29