We test more than 75 dishwashers in our specialist lab every year, cleaning more than 25,000 dirty dishes, glasses, cups and pieces of cutlery. But what goes on behind those walls and how is the score for each dishwasher generated?
Almost all free-to-access websites review dishwashers using an individual tester and generate scores based on that individual’s preferences. Free sites also typically get dishwashers free of charge directly from manufacturers or their PR representatives.
As well as using multiple testers in a lab-based scenario, the Which? overall percentage score is calculated purely on the measurements and ratings supplied by the lab, meaning there's no room for unconscious bias when giving an overall rating. We also buy every single product we test and do not accept free samples for any of our full lab tests.
Best Buys dishwashers impressed the most in our tests. Any full-size dishwasher that scores 75% or more is a Best Buy and comes with a firm overall recommendation, although you should still read our reviews to check for any weaknesses that might impact your buying decision. For slimline models, the threshold to be a Best Buy is 65%. Meanwhile, dishwashers that score less than 45% are made Don’t Buys.
If you want to make the most sustainable choice when next buying a dishwasher, an Eco Buy is for you.
Eco Buy dishwashers will have a lower impact on the environment over their lifetimes than other dishwashers.
We calculate this in three ways: how reliable and therefore long-lasting it's likely to be, so you don't have to repair or replace it as often; how energy efficient it is and how little water it uses.
To become an Eco Buy, a dishwasher must have:
The Which? overall score is a percentage. It only takes into account the results of our tests and ignores price completely. This means that all dishwashers are tested in exactly the same way so you can compare any, at any price, from any brand and know how it measures up against rivals.
A Which? overall score is made up of dozens of individual tests and checks, from key factors such as cleaning, drying and energy use, to ease of use and noise. This means that the most important things – such as how good a dishwasher can actually wash dishes – will impact a dishwasher’s score more than how noisy it is.
To keep things simple, the most important scores are shown as star ratings out of five on each dishwasher’s 'Test Results' page as an easy-to-compare list of strengths and weaknesses, so you can quickly work out whether it's the right model for you.
Below are the key testing categories and how we evaluate each one:
Key question: Can this dishwasher handle tough dirt and get everything dry?
To test how well each dishwasher cleans, we dirty a range of dishes, glasses, mugs and cutlery. Our menu of challenging grub and grime includes milk, tea, minced meat, eggs, oat flakes, spinach and margarine. We also let all the dirt dry on in a heated cabinet to simulate being sat on the side or in the dishwasher for a day before being being cleaned. This ensures we give every dishwasher a tough but realistic test.
We also add in some clean dishes to the load, to see if the dishwasher transfers grime - you wouldn’t want to buy a machine that just moves dirt from one plate to another.
After washing we inspect each item in the load and score the load for cleanliness and dryness, also paying attention to whether the dishwasher leaves water marks.
The best dishwashers leave every item spotless, dry and sparkling, while the worst deliver dirty wet dishes.
Cleaning, drying and not leaving water marks make up the bulk of our testing and account for 60% of the final Which? score.
Key question: Will this dishwasher actually be easier to use than just doing the washing up myself?
We load dishwashers with the kinds of stuff you most often want cleaned: large dinner plates, small plates, bowls, cups, knives, forks, tablespoons, teaspoons.
But we also add a collection more specific items to check whether the dishwasher can easily handle different shaped objects. These include serving bowls, a ladle, a saucepan, a shallow oven dish, a glass jug and a plastic lunch box.
We assess how easy it is to fill and empty each dishwasher to capacity, and whether it can accommodate large plates and long-stemmed wine glasses. We've found that some smaller slimline and table-top dishwashers can be harder to fill to capacity than their larger counterparts, although some full-sized models are a real chore to load, too.
Clear, well-labelled controls that make programming easy get the thumbs up from us. And because a good dishwasher is only great if it's effortless to use, we also check how easy it is to open and close the door, refill the salt and top up the rinse aid.
In 2020, we updated our testing to keep up with the latest dishwasher features. With more and more models including foldable prongs and other ways to make loading flexible, we now rate this and include it in our overall rating. This includes if you can fit in large plates and tall glasses at the same time.
Loading and control panel ease-of-use tests make up 15% of the total Which? score.
Key question: Will this dishwasher be kind on my utility bills as well as the environment?
We don't rely on the energy label to tell us how efficient a dishwasher will be. We run our own energy and water-use tests.
We do this on the main or auto program, which is likely to be the most commonly used setting. But we also test the energy-saving or eco programs for those that want to make an extra saving.
From this we calculate energy running costs for every model, so you know how much each dishwasher will affect your utility bills. The most efficient Best Buys are also named Eco Buys.
Energy and water use of both the main and eco program make up 20% of the total score.
Key question: Will it be a problem if the dishwasher is on while I'm trying to watch TV, listen to radio or have a conversation?
Dishwashers don't tend to be as loud as other appliances, such as vacuums, but a quieter model is an important consideration for those whose dishwasher sits in earshot of areas where people eat or relax, and also for those of us who like to run the dishwasher overnight.
We assess how noisy the filling and washing stages of each dishwasher are, listening out for any loud or particularly irritating noises or tones.
How quiet a dishwasher is makes up 5% of the score.
Front-loading dishwashers as we know them now first entered our kitchens back in the early 1960s. By the end of the 1970s, dishwashers were one of the most common home appliances. The Colston Mk4 was the first to become a Which? Best Buy in 1965.
Now each year we test more than 70 different machines by cleaning a whopping 25,000 dishes, bowls, cups, glasses and pieces of cutlery.
As you can see from the graph below, there is a wide variety in the scores of dishwashers in the same price bracket.
More expensive dishwashers tend to perform better, as you might expect, but we've found cheaper models that score higher than those that are twice the price.