Every conversion on this site derives from one relationship: an air fryer transfers heat to food faster than a conventional oven at the same dial setting, by roughly the equivalent of 25°F (15°C), and completes cooking in about 80% of the time. This page sets out where those figures come from, how they are tested, the seven conditions under which they stop holding, and what has been corrected since publication.
The physics the conversion is built on
Food in a hot oven is surrounded by a thin film of cooler, moisture-laden air clinging to its surface — the boundary layer. That film insulates. Heat has to cross it by conduction before reaching the food, and conduction through still air is slow.
Forced convection strips it away. Moving air continuously replaces the cooled, humid film with fresh hot air, so the surface sits much closer to the true cavity temperature and heat transfers substantially faster.
An air fryer does this aggressively — a fan at roughly two to three times the speed of a domestic convection oven, in a cavity a fraction of the size, with a perforated basket that lets air reach the underside. The practical result is that 375°F (190°C) in an air fryer browns and cooks like roughly 400°F (205°C) in a still-air oven.
Why 25°F (-5°C) and 20%
The two adjustments correct different things.
The 25°F (-5°C) temperature reduction compensates for the surface effect. Without it, the exterior browns and dries before the interior reaches temperature — the classic symptom of an unconverted recipe: burnt outside, raw inside.
The 20% time reduction compensates for the bulk effect. Faster surface heat transfer means a steeper thermal gradient into the food, so the centre reaches its target sooner.
Expressed as factors: temperature −25°F (−15°C), time × 0.8. Reversing the conversion uses +25°F (15°C) and × 1.25, which is the exact inverse. Using 20% in both directions would mean a recipe converted there and back never returns to its original numbers.
Where the figures come from
Published guidance. The 25°F (-5°C) reduction originates in convection oven practice, where it has been standard for decades and is printed in most oven manufacturers’ own manuals. Air fryers inherit it because they are high-velocity convection ovens.
Home-kitchen testing. Conversions are then cooked. Sarah tests them in her own kitchen; family and friends cook them in theirs, on different units at different wattages. A figure that works on one air fryer and not another is not published.
We are explicit that this is home testing, not laboratory testing. There is no calibrated test chamber behind these numbers. What there is: repeated cooking across several appliances, internal-temperature measurement for every protein, and the failure conditions published alongside the figures rather than omitted.
Proteins are judged by internal probe temperature, not appearance. Starches and vegetables are judged by texture and surface browning.
The convection exception
A convection oven already has forced air. Converting from convection to air fryer therefore corrects only the residual difference — fan velocity and cavity size — which is worth about 10°F (5°C) and 10% of the time, not 25°F (15°C) and 20%.
Applying the full conventional-oven adjustment to a convection recipe is the most common conversion error in circulation, and it undercooks.
Where the rule breaks down
We publish the limits because a rule presented without them produces failures readers blame on themselves.
| Condition | What happens | Adjustment |
|---|---|---|
| Below 325°F / 165°C | Underdone | Reduce 15–20°F (-5°C), not 25°F (-5°C) |
| Cakes and risen bakes | Sunken or raw centre | Reduce time 15%, not 20% |
| Cookies | Burnt top, raw middle | Reduce temperature 50°F / 10°C |
| Basket more than ⅔ full | Steamed and pale | Add 15–20% time, or split the batch |
| Unit under 1,400W | Underdone | Add roughly 10% time |
| Wet batter | Coating drips through before setting | Cannot be converted |
| Item over 4 lb / 1.8 kg | Exterior finishes far ahead of centre | Use an oven |
How we handle units
Every temperature appears in both Fahrenheit and Celsius. Conversions are calculated in the unit the recipe uses and only then displayed in the other — never converted across systems mid-calculation, which compounds rounding error at each step.
Celsius figures round to the nearest 5°C, because virtually no consumer air fryer offers finer increments. The 25°F (15°C) reduction is expressed as 15°C rather than the arithmetic 13.9°C for the same reason.
UK and Australian fan ovens are treated as convection ovens and take the 10°C adjustment. Gas marks map to the standard UK conventional table.
What has been corrected?
| Date | Figure | Change | Reason |
|---|---|---|---|
| REPLACE_DATE | Baked goods temperature reduction | 15°F (-10°C) → 50°F / 10°C | The smaller reduction browns the surface before the centre sets; cookies burn |
| REPLACE_DATE | General time factor | 0.75 → 0.80 | 0.8 is the exact inverse of the 1.25 used in the reverse direction |
| REPLACE_DATE | Celsius calculation | Cross-system → native | Converting °C to °F and back introduced about 5°C of drift |
Add each future correction here with the date and the reason. A visible corrections log is among the cheapest and strongest trust signals a reference site can carry, and almost nobody in this niche keeps one.
Related conversions and adjacent topics
Temperature and time convert together, never separately. The same rule set covers every appliance pair on this site, and the methodology page sets out where it comes from and the seven conditions under which it stops holding.
Every figure above is built into the oven to air fryer conversion calculator, which applies both adjustments together so you do not have to work them out separately.
Frequently asked questions
Where does the 25°F (-5°C) rule come from?
Convection oven guidance, where 25°F (-5°C) has been the standard reduction from conventional temperatures for decades. Air fryers inherit it because they are high-velocity convection ovens.
Are these figures laboratory tested?
No. They are tested in home kitchens across several air fryer models, with internal-temperature checks for proteins, and cross-referenced against published manufacturer guidance.
Why does your convection figure differ from other sites?
Many sites apply the full 25°F (-5°C) conventional reduction to convection recipes. That double-counts the fan a convection oven already has, and undercooks the food.
Do these figures apply to every air fryer?
To most. Wattage below 1,400W or above 1,700W shifts timing by roughly 10% in each direction, which is why the calculator includes a wattage note.
How do I report a figure that did not work?
Email hi@oventoairfryerconverter.com. Corrections are logged above with the date and reason.