Dishwasher or hand washing: the right question

Many people think washing up by hand is cheaper because "the dishwasher uses electricity". In fact hand washing uses energy too: the energy needed to heat the water. This calculator compares the cost of a dishwasher load with the cost of washing the same load by hand, and shows the annual saving and the water saved.

It works in any currency: enter the energy price per kWh and the water price per cubic metre from your bills.

How the calculation works

You enter how many loads you run a week, your dishwasher's kWh and litres per cycle, the litres you would use by hand to wash the same amount of dishes, the energy price and the water price.

• Dishwasher cost: kWh per cycle × energy price + litres per cycle × water price / 1000.
• Hand-washing cost: litres × energy to heat them × energy price + litres × water price / 1000.
• Energy to heat the water: a declared convention of 0.029 kWh per litre, the energy to bring one litre from 15 to 40 °C.
• Annual saving: the difference per load multiplied by the loads over 52 weeks.

The verdict is based on the dishwasher's cost as a percentage of hand washing: a ratio that depends neither on the currency nor on how many loads you run.

The litres at the sink decide everything

The table keeps a modern dishwasher fixed (0.9 kWh and 11 litres per cycle, 0.292 per load with energy at 0.30 and water at 2 per cubic metre) and changes the litres used by hand for the same load, with five loads a week.

The break-even point is around 27 litres of hot water per load. Washing with two basins can stay below it; washing under running water passes it within minutes, because an open tap often delivers 6 to 12 litres a minute. That is why, in most homes, a full dishwasher uses less.

The energy price matters little

It is natural to think that with expensive energy hand washing pays. But energy weighs on both sides: the dishwasher heats its small amount of water, hand washing heats much more. The table uses 60 litres by hand and the same dishwasher.

Quadrupling the energy price moves the ratio by less than ten points. What changes the result is not the bill, it is how you wash.

The water saved

Besides money, the calculator shows the litres of water saved in a year. With 60 litres by hand against 11 in the dishwasher, each load saves 49 litres.

A study by the University of Bonn, which watched dozens of people in several European countries wash by hand the same amount of dishes as a full dishwasher, found average water and energy use far higher than the machine's, with huge differences from one person to another.

Getting the most from the dishwasher

The dishwasher's advantage holds when it is full: a half-empty cycle costs almost as much as a full one. The eco programme uses lower temperatures and longer cycles, and is usually the most efficient. There is no need to rinse dishes under running water before loading them: scraping off solid leftovers is enough, otherwise you add exactly the consumption of hand washing.

The five bands of the verdict

• Hand washing costs less: this happens with very little water or with an old, inefficient dishwasher.
• Below 30%: the dishwasher wins by a mile.
• 30% to 50%: the dishwasher clearly pays.
• 50% to 75%: it pays, but with a moderate margin.
• Above 75%: the cost almost evens out, and time, hygiene and convenience decide.

Where to find your dishwasher's figures

The energy label shows energy use per hundred cycles and the litres per cycle of the eco programme: divide the energy by a hundred to get kWh per cycle. If the machine is very old and has no label, manuals for models fifteen or twenty years old often state 1.2–1.5 kWh and 15–20 litres. For litres by hand, the easiest way is to count them once: fill a basin, or time how long the tap stays open.

Limits of the calculator

The model uses a fixed convention for the energy needed to heat water and assumes all hand-washing water is hot and heated at the same energy price as the dishwasher's. It does not include detergent, the purchase price of the machine, boiler efficiency or the time spent. If you heat water with gas, you can enter the cost of gas per kWh as the energy price for an approximation.

Frequently asked questions

Is a dishwasher cheaper than washing by hand?

In most homes a full dishwasher costs less, because hand washing means heating much more water. The calculator tells you by how much in your case.

Why does hand washing use energy?

Because hot water has to be heated: bringing one litre from 15 to 40 degrees takes about 0.029 kWh. With 60 litres that is about 1.7 kWh per load, more than a modern dishwasher uses.

How many litres does hand washing use?

It depends heavily on the method: with two basins you can stay under 30 litres, with running water you easily exceed 50 or 100, because an open tap often delivers 6 to 12 litres a minute.

What is the break-even point?

With a modern dishwasher at 0.9 kWh and 11 litres, energy at 0.30 and water at 2 per cubic metre, break-even is around 27 litres of hot water per load washed by hand.

With expensive energy, does hand washing pay?

Rarely: energy weighs on both methods. Quadrupling the energy price moves the ratio by only a few points; the litres used by hand decide.

Where do I find my dishwasher's kWh and litres?

On the energy label: it shows energy per hundred cycles, to divide by a hundred, and litres per cycle for the eco programme. Otherwise in the manual.

Does a half-empty dishwasher still pay?

Much less: a half-empty cycle uses almost as much as a full one. The dishwasher's advantage holds mainly when it is full.

Should I rinse dishes before loading them?

No, scraping off solid leftovers is enough. Rinsing under running water adds exactly the hand-washing consumption the dishwasher is meant to avoid.

Does the calculator include detergent?

No. Tablets and washing-up liquid have different but usually small costs compared with energy and water; the calculator leaves them out for simplicity.

What if I heat water with gas?

Enter the cost of gas per kWh as the energy price: you get an approximation. The calculator does not account for boiler efficiency.

How much water do I save in a year?

The difference in litres per load times the loads in a year. With 60 litres by hand, 11 in the dishwasher and five loads a week, that is about 12,700 litres.

Does it work in any currency?

Yes. Enter energy and water in the same currency; the verdict is based on a percentage that does not depend on the currency.