It's just convection, moving fast
A convection oven circulates hot air to cook food more evenly than a still-air oven. An air fryer does the same thing in a box one-tenth the size, with a fan sized aggressively for the volume. The hot air moves faster past the food, which means two things: surfaces dehydrate more quickly, and heat transfer to the food's interior speeds up as well.
That first effect — surface dehydration — is what everyone means when they say air fryers "crisp." The fan strips moisture away from the outside of the food, and a dry, hot surface browns. The Maillard reaction (proteins and sugars reacting at high temperatures) and caramelization (sugars breaking down) both need a dry surface to proceed, so an air fryer naturally hits those reactions faster than a regular oven.
There is no frying. There never was.
The name is marketing. Deep frying cooks food by submerging it in oil at 325–375°F, where water inside the food flashes to steam and gets pushed out as oil coats the surface. Air "frying" does none of that. It dries and browns the outside via hot air. The textures can be similar — both produce a crisp shell — but they are not the same physical process, and recipes do not translate one-to-one.
This matters in practice. Battered foods that were designed for the deep fryer will generally not crisp up the same way in an air fryer, because the batter was engineered for oil immersion. Frozen foods that were parfried before freezing (most store-bought fries, mozzarella sticks, breaded chicken) do great, because the fat is already in the coating. Anything that was wet-battered at home is a toss-up.
Why the 20/20 rule is a starting point, not a promise
The popular conversion is "drop 20 degrees, cut time by 20%." That works for a lot of food because air fryers are fast and hot, but it assumes a standard-size basket-style fryer and a generic piece of food. The reality is messier:
- Cheaper basket fryers run 10–20°F hotter than their dial says. Premium models run cooler and more accurately.
- High-wattage fryers (the Ninja Foodi line, for example) heat up in a minute and cook 10–15% faster than a standard 1500W unit.
- Oven-style air fryers behave almost like small convection ovens, so the 20/20 rule barely applies — they need closer to a 15°F drop and 10% less time.
- Food matters too: a dense piece of raw chicken cooks differently from a layer of frozen fries, and neither behaves like a tray of cookies.
Our calculator builds these modifiers in so you don't have to memorize them. Pick the food type and the fryer model and it adjusts the base conversion automatically.
What this means when you're cooking
A few practical takeaways that fall out of the physics:
- Dry the food. Any surface moisture is heat the fryer has to evaporate before it can brown anything. Paper towels matter more than a fancy rub.
- Don't crowd the basket. Steam from one piece soaks the next one. Cook in rounds if you have to — the second round is faster because the fryer is already hot.
- Preheat if you want a brown outside and a juicy inside. A cold start means the surface spends too long at a moderate temperature, which overcooks the interior before the outside gets dry.
- Open the basket. The fan can't circulate around wings if they're glued together; a mid-cook shake is how the second side gets cooked at all.