Dishwasher vs handwashing: a cost-per-load comparison with the maths shown
Whether a dishwasher costs more or less than handwashing depends on how much hot water you use. You can compare them with a short calculation.
Heating water costs energy
Heating one gallon of water by 60 degrees Fahrenheit takes roughly 500 BTU, which is about 0.147 kWh of electricity if heated electrically with no losses. Heating ten gallons is therefore about 1.47 kWh.
Worked example
| Dishwasher load | Handwashing | |
|---|---|---|
| Water used | 4 gallons | 10 gallons of hot water |
| Energy | 1.2 kWh (including heating) | 1.47 kWh to heat the water |
| Electricity | $0.20 | $0.25 |
| Water | $0.04 | $0.10 |
| Cost per session | about $0.24 | about $0.35 |
In this example the dishwasher is cheaper per session, but the result depends on how you wash. Running the tap while rinsing can use far more water than the assumption above, while running a half-empty dishwasher wastes its fixed cost.
To make your own comparison
- Find your dishwasher's energy and water use per cycle in the manual or label
- Estimate how many gallons of hot water you use by hand
- Use your own electricity and water prices
- Count detergent and your time, which are not included above