๐ซ Electric Kettle Boil Time Calculator
If you don't know the efficiency, around 90% is a reasonable estimate.
Enter the volume of water (mL), starting and target temperature, and your electric kettle's wattage to estimate how long it will take to heat, based on the specific heat of water (4.186 J/gยฐC).
How to use
- Enter the volume of water to boil (mL).
- Enter the kettle's power consumption (W).
- Enter the starting and target temperature (usually 100ยฐC).
- Enter the heating efficiency (%) โ around 90% is a reasonable default if unknown.
How the calculation works
Estimate how long an electric kettle takes to heat water from the amount, starting and target temperatures and the kettleโs power. Heat needed (J) = water (g) ร 4.186 ร temperature rise (ยฐC) Time (s) = heat รท (power (W) ร efficiency) 4.186 is the specific heat of water, the energy to raise 1 g by 1 ยฐC. Efficiency accounts for heat that warms the kettle itself or escapes; around 80โ90% is typical for electric kettles. The target can be at most 100 ยฐC.
Worked example
1000 mL of water, 20 ยฐC โ 100 ยฐC, 1200 W, 90% efficiency 1000 ร 4.186 ร 80 รท (1200 ร 0.9) โ 310 s (about 5 min 10 s) Under the same conditions, 500 mL takes about 2 min 35 s, and heating to 80 ยฐC takes about 3 min 53 s. Boiling only what you need saves both time and electricity.
Things to be aware of
- Tap water in winter is 5โ10 ยฐC, so it takes longer to boil than in summer.
- At altitude water boils below 100 ยฐC (about 87 ยฐC on top of Mount Fuji).
- Kettles draw a lot of power at once, so running one alongside other appliances can trip the breaker.
FAQ
What formula does this use?
It uses the basic physics formula Q (joules) = mass (g) ร specific heat of water (4.186 J/gยฐC) ร temperature change (ยฐC), then divides by the effective wattage (power ร efficiency) to get time.
Why does efficiency matter?
In a real kettle, some power is lost to heating the container and the surrounding air rather than the water itself, so the actual time is longer than the theoretical value. The efficiency factor corrects for this.
Does this assume water is 1g per mL?
Yes โ water near room temperature is close enough to 1mL = 1g for this calculation.