Electric Kettle vs Stovetop Boiling Cost Calculator

The model, stated exactly

Useful heat per litre = 1 kg × 4.186 kJ per kg per °C × 80°C = 334.88 kJ, rounded to 335 kJ (0.09306 kWh). Input energy = useful heat ÷ efficiency: kettle 85%, electric coil 70%, gas burner 40%. Electric cost per boil = input kWh × electricity rate per kWh. Gas cost per boil = input kWh-equivalent ÷ 29.3 kWh per therm × gas price per therm. Annual cost = boils per day × 365 × cost per boil, computed from the unrounded per-boil cost and then rounded to cents. Time is context only, not a cost input: a kettle takes roughly 3–4 minutes per litre and a stovetop pot roughly 8–10 minutes, so the kettle saves about 4–7 minutes per boil, or roughly 73–128 hours of waiting a year at 3 boils a day. The comparison is energy cost only: it excludes buying any appliance, and it assumes the same starting temperature (20°C) and the same volume for all three methods.

The worked example, line by line

Setup: 1 litre, 3 boils a day, $0.17 per kWh, $1.75 per therm.

Line 1 — useful heat. 1 × 4.186 × 80 = 334.88 kJ, rounded to 335 kJ = 0.09306 kWh.

Line 2 — kettle input energy. 0.09306 ÷ 0.85 = 0.10948 kWh per boil.

Line 3 — kettle cost per boil. 0.10948 × $0.17 = $0.019 per boil.

Line 4 — coil input energy. 0.09306 ÷ 0.70 = 0.13294 kWh per boil.

Line 5 — coil cost per boil. 0.13294 × $0.17 = $0.023 per boil.

Line 6 — gas input energy. 0.09306 ÷ 0.40 = 0.23264 kWh-equivalent per boil.

Line 7 — gas cost per boil. 0.23264 ÷ 29.3 × $1.75 = $0.014 per boil.

Line 8 — boils per year. 3 × 365 = 1,095 boils a year.

Line 9 — annual costs. 1,095 × $0.019 = $20.38 kettle; 1,095 × $0.023 = $24.75 coil; 1,095 × $0.014 = $15.21 gas (each computed from unrounded per-boil costs, then rounded).

Line 10 — the verdict. The kettle saves $4.37 a year over the coil ($24.75 − $20.38) but costs $5.16 a year more than gas ($20.38 − $15.21).

Try these

Just 1 boil a day. 365 boils a year cost $6.79 kettle, $8.25 coil, and $5.07 gas — at this volume the whole argument is worth about $3 a year, so pick on speed and convenience.

6 boils a day. 2,190 boils a year cost $40.76 kettle, $49.49 coil, and $30.43 gas — heavy users save $8.73 a year by choosing the kettle over the coil, and $10.33 by choosing gas over the kettle.

Electricity at $0.30 per kWh. The kettle costs $0.033 per boil and the coil $0.040, while gas stays at $0.014 — expensive electricity makes gas the runaway winner on price.

A 2 litre pot. Every per-boil cost doubles: kettle $0.037, coil $0.045, gas $0.028 — and at 3 boils a day the annual totals become $40.76, $49.49, and $30.43, the same as the 6-boil case because both double the yearly volume.

Output · formula · meaning

Who uses this

• The tea drinker choosing a kettle: enters 3 boils a day and learns the kettle saves $4.37 a year over the coil — then decides the real win is 4–7 minutes saved per boil, not the dollars.
• The renter with a gas stove wondering whether to buy a kettle: enters their gas price and sees gas is still $5.16 a year cheaper — so the kettle purchase has to be justified by speed, not savings.
• The household on expensive electricity: enters $0.30 per kWh and sees the kettle at $0.033 and the coil at $0.040 per boil, which makes gas at $0.014 the clear price winner.
• The pasta household boiling big pots: enters 2 litres and learns a full pot costs $0.037 in the kettle versus $0.028 on gas — and that a kettle only helps if the pot fits under it.

Accuracy & limitations

The physics is exact for the stated assumptions, but four of them deserve daylight. First, the efficiencies (85%, 70%, 40%) are realistic planning figures, not measurements of your appliances: a limescaled kettle, a warped pot bottom, or a pot much wider than the burner all waste more heat, and an induction hob (not modeled here) runs closer to 85–90% because it heats the pot directly. Second, the starting temperature is assumed to be 20°C; cold tap water at 10°C needs about 12% more heat, and already-warm water needs less. Third, the gas figure depends on your gas price per therm and on the 29.3 kWh-per-therm conversion — if your bill quotes gas per cubic metre or per gigajoule instead, convert it first. Fourth, time figures (3–4 versus 8–10 minutes) are typical ranges, not measurements: a powerful kettle boils a litre in under 3 minutes, and a covered pot on a strong burner is faster than an uncovered one on a weak burner. Error policy: missing, non-numeric, or out-of-range inputs (litres outside 0–20, boils outside 0–50, electricity rate outside 0–$2, gas price outside 0–$20) are reported as errors rather than calculated, so no result ever shows NaN.