An air fryer is a small fan oven
Everything about the conversion follows from that one sentence, and so does everything that goes wrong. A fan drives hot air onto the food, so it cooks faster at a lower dial setting. A small cavity gets to temperature in two minutes instead of fifteen. The fan is closer and harder than an oven's, so surfaces dry and brown quickly.
So the conversion is the fan deduction, plus about a fifth off the clock, plus checking well before either. Nothing more complicated is going on, and any chart implying otherwise is dressing up two lines of arithmetic.
The deduction depends on where you learned it
Britain publishes the fan reduction as 20°C. North America publishes it as 25°F. Those sound like the same instruction in different units and they are not, because 20°C is 36°F. From a 200°C oven the British rule gives 180°C and the American rule gives 375°F, which is 190°C. Ten degrees apart, on the same machine.
Neither is measured. They are two kitchens' rules of thumb, and the switch on this page gives you the one your own manual is written against rather than quietly picking.
The list nobody publishes: what does not transfer
Every conversion chart online implies that everything moves across. Plenty does not, and the reasons are physical rather than fussy.
Wet batter. It runs through the basket before it can set, because there is nothing underneath it but holes and a drip tray. Yorkshire puddings, tempura, beer-battered fish. A dry crumb coating is a different proposition entirely and is close to the perfect air fryer food.
A large joint. Not a space problem, an evenness problem. The surface sits inches from a hard fan while the centre is a long way from anything, so the outside is done well before the middle. About 1.5 kg is where this starts to bite.
Anything that needs liquid. Rice, pasta, pulses, stews, soups, curries. It is not that they are slow in an air fryer, it is that there is nowhere to keep the liquid. This is the one people try anyway.
Leaves and light herbs. They blow around, because the fan is the whole appliance. Kale crisps are the standard exception and only work weighted under a rack.
Bread and anything with a long rise. The fan sets the crust long before the inside has finished expanding, so it stops rising with a raw middle.
One layer, and the real limit is floor space
This decides more than the temperature does and no chart mentions it. The basket has to be loaded in a single layer with nothing overlapping. Fill it up and the fan cannot reach most of the food, so it steams in its own moisture, and steaming is the exact opposite of the one thing you bought the machine for.
Which means the honest answer to "can I do this in the air fryer" is frequently "yes, in two batches". A tray of roasting vegetables that fits one oven shelf is two or three basket loads. That is not a failure of the appliance, it is the size of it, and the second batch goes faster because the machine is already hot.
The two problems everybody hits in the first month
Nothing is crispy. The basket is too full, nine times out of ten. The tenth is not preheating: food going into a cold basket spends its first few minutes drying in moving air without colouring, which gives you pale and leathery rather than crisp. Two minutes of preheat fixes it.
The kitchen is full of smoke. Fat is dripping onto the element under the basket. Burgers and fatty sausages do it reliably. A few tablespoons of water in the drawer underneath means the drips land in liquid instead of on hot metal, and it is worth doing before you need it, because once it starts the only cure is stopping and cleaning.
Common questions
How do I convert oven time and temperature to an air fryer?
Drop the temperature the way you would for a fan oven and take about a fifth off the time, then check well before either number. An air fryer is a small fan oven, so everything follows from that. The temperature deduction is 20°C if you learned it in Britain and 25°F if you learned it in North America, which are not the same size, and this tool gives you whichever your own manual publishes.
Can you put batter in an air fryer?
Not a wet one. Batter runs through the holes in the basket before it has any chance to set, and what lands in the drip tray is a mess rather than dinner. That rules out Yorkshire puddings, tempura and beer-battered fish. A dry crumb coating is a completely different thing and is close to the ideal air fryer food, which is why frozen breaded anything comes out so well.
Why is my air fryer food not crispy?
Almost always because the basket is too full. A crowded basket steams, since the fan cannot reach most of the food, and reaching the food is the only thing the appliance does. One layer, nothing overlapping, and cook in two batches if you have to. The second batch is faster because the machine is already hot, so it costs you less time than it sounds.
How big a chicken fits in an air fryer?
About 1.5 kg in a larger basket, and that is a limit on evenness rather than on space. In a cavity that size the surface of the bird is inches from a hard fan while the middle is a long way from anything, so a bigger bird browns hard outside before the thigh joint is done. Cook breast down for the first half and check with a probe at the joint rather than trusting a time.
Why does my air fryer smoke?
Fat dripping onto the hot element under the basket. Burgers and fatty sausages are the usual culprits, and the fix is a few tablespoons of water in the drawer beneath, so the drips land in liquid rather than on metal. It is worth doing before it happens, because once the smoke starts the only cure is stopping and cleaning it.
Can you cook rice or pasta in an air fryer?
No, and this is not a matter of it being slow. Both need to sit in boiling liquid and an air fryer has nowhere to keep liquid: it is a fan and a basket over a drip tray. The same goes for stews, soups and anything with a sauce. Air fryer rice recipes exist and they all involve a separate tin of water inside the basket, which is an oven doing an oven job badly.
Is an air fryer the same as a convection oven?
It is a small one with a harder fan, and the difference is almost entirely size. Less air to heat means it reaches temperature in a couple of minutes rather than fifteen, and the food is much closer to the fan, so surfaces dry and brown faster. That is also the limitation: a small cavity is a small cavity, and everything that goes wrong in one is a consequence of the space rather than the technology.
Do you need to preheat an air fryer?
For anything you want browned, yes, and it takes two or three minutes rather than fifteen. Putting food into a cold basket means it spends the first few minutes warming through in moving air, which dries the surface without colouring it, so chips come out pale and leathery. For a longer cook where browning is not the point, it matters much less.
Does an air fryer use less electricity than an oven?
For small quantities, usually yes, and the reason is size rather than efficiency. There is far less air and metal to bring up to temperature and the cook is shorter, so less energy goes in. The saving disappears as the quantity grows: three basket loads one after another is not obviously cheaper than one oven shelf, and if you were going to use the oven for something else anyway it was already paid for.