What Is the 25 Rule for Air Fryers? (The Complete Conversion Guide)

You grab your favorite oven recipe. You load the air fryer. You set the same temperature — and 20 minutes later, dinner is burnt on the outside and raw in the middle. Sound familiar?

I’m Chef Emma, and I’ve cooked in professional kitchens and home kitchens for over 15 years. The most common air fryer mistake I see? People don’t adjust their oven recipes. They just drop the same numbers in and hope. That’s what the 25 rule fixes.

This guide covers the full 25 rule — what it is, why it works, when to follow it, and when to break it. By the end, you’ll know exactly how to convert any oven recipe for your air fryer without guessing.

What Exactly Is the 25 Rule for Air Fryers?

The 25 rule is the standard formula for converting oven recipes to air fryer settings. Reduce the oven temperature by 25°F and reduce the cooking time by 20%. That’s it. Most experts — including air fryer cookbook author Linda Larsen — agree this is the right starting point for almost any fresh food.

Here’s the math in plain terms. If your oven recipe says 400°F for 30 minutes, set your air fryer to 375°F. Then multiply 30 by 0.8. That gives you 24 minutes. So your new air fryer settings are 375°F for 24 minutes. You check at the 12-minute halfway point. Simple.

These numbers are starting points — not exact guarantees. Every air fryer model heats slightly differently, which is why checking at the halfway mark matters every single time.

Why Does the 25 Rule Work? The Science Behind It

Air fryers cook faster than ovens because they use rapid air circulation technology — a high-speed fan pushes superheated air around food inside a small, enclosed chamber. This constant movement of hot air hits every surface of the food at once. A standard oven heats a large cavity with much less airflow, so heat transfer is slower and less intense.

The technical name for the process inside a Philips air fryer (the brand that invented the category in 2010) is Rapid Air Technology. The science behind it combines thermal radiation from the heating element with forced convection from the fan. This combination triggers the Maillard reaction — the browning process that creates a crispy crust — faster than a conventional oven does. That’s why food gets golden and crispy in an air fryer without being submerged in hot oil.

So what does that mean for your cooking? A conventional oven at 400°F and an air fryer at 375°F deliver the same effective heat to your food. The lower setting in the air fryer is not underpowered — it’s calibrated for the intense airflow. If you don’t reduce the temperature, the food’s exterior overcooks before the inside is done.

Does the 25 Rule Apply to Frozen Food in an Air Fryer?

For frozen food, the 25 rule changes. Keep the temperature the same as the package instructions — but still reduce the time. Frozen foods like chicken nuggets, french fries, fish sticks, and pizza rolls need full heat to crisp their coating properly. The coating won’t brown correctly at a lower temperature.

Most frozen foods cook in 30 to 40% less time than the package oven instructions — not the standard 20%. So for a bag of frozen fries that says 25 minutes at 400°F in the oven, set your air fryer to 400°F and start checking at 15 minutes. They’ll likely be done around 16 to 18 minutes.

Here’s why this matters. I once followed the full 25 rule on frozen wings — dropped the temp to 375°F — and the coating never crisped up the way it should have. The coating needs that blast of full heat to set. Once I switched back to the package temperature and cut just the time, the wings came out perfect every single time.

When Does the 25 Rule Break Down?

The 25 rule is a great starting point — but it’s not a law of physics. Four food types cook differently enough that you need to adjust your approach. Knowing when to bend the rule saves dinner.

Thin, delicate foods like tilapia fillets, asparagus spears, and thin-sliced vegetables cook extremely fast. These can go from perfectly done to overdone in 60 to 90 seconds. Start checking them at 5 minutes, regardless of what the conversion formula says. Check every minute after that.

High-heat searing is the one case where you don’t lower the temperature at all. If you’re cooking a thick steak and want a proper crust, keep the air fryer at the full oven-equivalent heat — 400°F or higher. Just reduce the time. The crust needs that high heat to form the Maillard reaction properly.

Thick, dense foods like whole chicken, thick pork roasts, or a large potato might need slightly more time than the 20% reduction gives them. The outside cooks faster than the inside. Use a meat thermometer to check the internal temperature rather than relying on time alone. USDA guidelines require chicken to reach 165°F internally — that’s the only number that guarantees safety.

Baked goods need extra care. Cakes, muffins, and brownies in an air fryer will brown on top very fast because the fan pushes intense heat directly down. Cover the top loosely with a small piece of foil after the first 5 minutes to prevent burning while the inside finishes baking.

What Most People Get Wrong About the Air Fryer 25 Rule

Most people think the 25 rule is a formula that always works on its own. It doesn’t. The rule gives you a starting number — you still need to check the food. Treating it as a guaranteed result rather than a guide is the single biggest mistake I see.

Wrong belief #1: The 25 rule works whether the basket is full or not. It doesn’t. If you stack food in the basket, hot air can’t circulate freely. The rule assumes a single layer. A crowded basket needs more time — and still won’t cook evenly. The rule only works the way it’s meant to when food sits in one flat layer with space around each piece.

Wrong belief #2: You don’t need to preheat an air fryer. You do. A cold air fryer takes 2 to 3 minutes to reach the set temperature. If you add food to a cold basket, the first few minutes of your converted time are wasted warming the machine. Preheat for 3 to 5 minutes before adding food — always. This is the step most beginners skip and then wonder why their results are inconsistent.

Wrong belief #3: The 25 rule applies the same to Celsius and Fahrenheit. It doesn’t — not exactly. The 25°F reduction equals about 15°C. If your air fryer displays Celsius, subtract 15°C from the oven recipe — not 25°C. A 180°C oven recipe becomes 165°C in the air fryer, with time reduced by 20%.

Is This Right for Me? How to Choose Your Conversion Approach

Not every kitchen situation calls for the exact same approach. Here’s how to decide.

• If you’re converting a fresh oven recipe → reduce temp by 25°F and time by 20%. Check halfway.
• If you’re cooking frozen packaged food → keep the package temperature, reduce time by 25 to 30%.
• If you’re baking in an air fryer → reduce temp by 25°F, time by 20%, and cover the top with foil at the 5-minute mark.
• If you’re searing meat at high heat → keep full oven temperature, only reduce the time.
• If you’re cooking very thin foods → reduce temp by 25°F, but check starting at 5 minutes.

This article covers converting oven and standard frying recipes. If you’re adapting a slow cooker recipe or a microwave recipe for the air fryer, the conversion is different — those recipes are built on steam-cooking, not dry heat.

How to Get Crispy Results Every Time With the 25 Rule

The 25 rule sets the temperature and time. But these 3 habits determine whether results are actually crispy — or just cooked.

Use a light oil coat. A quick spray of oil on fresh food — about 1 to 2 teaspoons — helps the Maillard reaction happen faster and more evenly. Without any oil, fresh foods like chicken or vegetables can dry out instead of crisping. Frozen foods already have oil in their coating, so they don’t need extra.

Shake or flip halfway through. For small items like fries, nuggets, or cut vegetables, shake the basket at the halfway point. For larger items like a chicken breast or pork chop, flip it. Hot air still has a slight directional bias — the top surface browns first. Flipping ensures both sides crisp the same way.

Don’t open the basket constantly. Every time you open the basket, hot air escapes and the temperature drops. Check once at the halfway mark. Check once near the end. That’s it.

What About Deep Fryer to Air Fryer Conversion?

Converting a deep fryer recipe to an air fryer uses a slightly different version of the 25 rule. Reduce the temperature by 25°F — same as with oven recipes. But the time is roughly the same as or slightly longer than the deep fryer time, not shorter. Deep fryers cook in oil at high temperatures and very fast. Air fryers are efficient, but they’re not that fast.

For example, a deep fryer recipe for chicken wings at 350°F for 10 minutes becomes 325°F in the air fryer — but plan for 15 to 18 minutes. Check at 12 minutes and go from there. Since most deep fryer times are very short (5 to 12 minutes), you may only add 2 to 5 minutes rather than cutting time.

Does Preheating Matter When Using the 25 Rule?

Preheating changes your results more than most people expect. A cold air fryer basket slows down the first few minutes of cooking. The 25 rule conversion assumes the machine is already at temperature when the food goes in. If it isn’t, the food spends extra time in a warming chamber instead of a cooking chamber — and the conversion math no longer holds.

Preheat for 3 to 5 minutes at the target temperature before adding any food. This one step makes your 25 rule conversions consistent and predictable. It’s the habit that separates cooks who get reliable results from those who don’t.

How Do You Convert Celsius Oven Recipes for an Air Fryer?

If your recipe uses Celsius, subtract 15°C from the oven temperature and reduce the time by 20%. A recipe at 180°C for 25 minutes in the oven becomes 165°C for 20 minutes in the air fryer. Most European and UK recipes use Celsius, so this conversion matters for a large share of online recipes.

One thing worth knowing: some air fryers only display Fahrenheit. If you own one of those, convert your Celsius oven temperature to Fahrenheit first (multiply by 1.8, then add 32), then apply the standard 25°F reduction. It’s one extra step, but it only takes 10 seconds.

For a 180°C recipe in Fahrenheit: 180 × 1.8 + 32 = 356°F. Subtract 25 = 331°F. Round to the nearest setting on your air fryer — usually 325°F or 330°F. Multiply 25 minutes by 0.8 = 20 minutes. Done.

Conclusion

The 25 rule — reduce temperature by 25°F and cooking time by 20% — gives you a reliable starting point for any oven-to-air-fryer conversion. But the rule only works when you preheat the machine, cook in a single layer, and check at the halfway mark. Those three habits make the difference between consistent results and guesswork.

The one thing most guides won’t tell you: the 25 rule is a formula for control, not a promise of perfection. Your specific air fryer model, your basket size, and the thickness of what you’re cooking all affect the final result. The first time you cook a new recipe is always a test run — write down what worked and adjust from there.

Right now, take one oven recipe you’ve been wanting to try. Apply the 25 rule: subtract 25°F from the temperature, multiply the time by 0.8, preheat for 4 minutes, and check at the halfway point. That first conversion is the one that builds confidence. — Chef Emma

Frequently Asked Questions

What is the 25 rule for air fryers in simple terms?

The 25 rule means lowering your oven recipe’s temperature by 25°F and reducing the cooking time by 20% when using an air fryer. For example, 400°F for 30 minutes in an oven becomes 375°F for 24 minutes in an air fryer. The rule works because air fryers circulate hot air rapidly in a small space, cooking food faster than a standard oven.

Does the 25 rule apply to frozen food in an air fryer?

For frozen food, keep the temperature the same as the package oven instructions but cut the time by 20 to 30%. Frozen coatings and breading need full heat to crisp properly — lowering the temperature makes them soggy instead of crispy. Check frozen food earlier than you think you need to.

How do I convert an oven recipe to Celsius for my air fryer?

Subtract 15°C from the oven temperature and reduce the cooking time by 20%. A 180°C oven recipe becomes 165°C in the air fryer, with the time reduced by 20%. If your air fryer only shows Fahrenheit, convert the Celsius temperature first, then apply the standard 25°F reduction.

Why is my air fryer food not crispy even when I use the 25 rule?

The most common causes are an overcrowded basket, skipping the preheat, or not drying the food surface before cooking. The 25 rule requires a single layer of food and a preheated machine to work correctly. Pat fresh food dry, lightly coat with oil, and always preheat for 3 to 5 minutes before adding food.

Can I use the 25 rule for baking in an air fryer?

Yes — reduce the oven temperature by 25°F and the time by 20%, same as any oven recipe. The extra step for baking is to cover the top of your dish loosely with foil after the first 5 minutes to prevent the top from burning while the inside bakes through. The fan-driven heat browns the top of cakes and muffins much faster than a standard oven.