Baking Time and Temperature Conversion Chart
To convert a recipe written for 350°F, drop the temperature about 25°F and cut the time by roughly 25 percent if you are switching to a convection (fan) oven — so a 40-minute bake at 350°F becomes about 30 minutes at 325°F. Going the other way, from convection back to conventional, raise the temperature about 25°F and add time back. Always confirm doneness rather than trusting the converted number alone.
Recipes also get converted between whole-number Fahrenheit steps — 325, 350, 375, 400, 425°F — when a dish needs to share oven space with something baking at a different setting. Every 25°F step up shortens time by roughly 10–15 percent for most baked proteins and vegetables, though delicate baked goods like cakes and custards convert less predictably and are better left at their written temperature.
For any meat or poultry dish, temperature conversion changes cooking time but never changes the required safe endpoint. Whole poultry still needs 165°F (74°C), ground meats 160°F (71°C), and whole cuts of beef, pork, lamb and veal 145°F (63°C) plus a 3-minute rest, per the USDA FSIS safe minimum internal temperature chart. A converted time is only a starting estimate — the thermometer has the final word.
Fahrenheit to Celsius Conversion
| Fahrenheit | Celsius (rounded) | Common Use |
|---|---|---|
| 300°F | 149°C | Slow roasting, low-and-slow meats |
| 325°F | 163°C | Casseroles, gentle baking |
| 350°F | 177°C | Most everyday baking |
| 375°F | 191°C | Roasting vegetables, chicken pieces |
| 400°F | 204°C | Faster roasting, crisping |
| 425°F | 218°C | High-heat roasting, browning |
| 450°F | 232°C | Pizza, very fast bakes |
Round to the nearest 5°C when your oven dial only shows Celsius in five-degree steps; the difference of a degree or two rarely changes results in home baking.
Conventional to Convection (Fan) Oven Conversion
| Conventional Temp | Convection Temp | Time Adjustment | Timer |
|---|---|---|---|
| 350°F (177°C) | 325°F (163°C) | Reduce by about 25% | |
| 375°F (191°C) | 350°F (177°C) | Reduce by about 20% | |
| 400°F (204°C) | 375°F (191°C) | Reduce by about 15–20% |
Fan ovens move hot air continuously across food, so heat transfers faster and browns surfaces sooner. Manufacturers rarely agree on exact numbers, so treat these as a starting adjustment and check five minutes earlier than the converted time suggests.
What Changes the Conversion
Dish density and depth
A shallow, single layer of food (thin cutlets, sliced vegetables) responds fastest to a fan setting, since air reaches more of the surface. A deep casserole or a whole roast benefits less from the fan and may need a smaller time cut than the general rule suggests.
Oven calibration
Home ovens commonly run 15–25°F off their dial reading in either direction. An inexpensive oven thermometer hung on the center rack reveals your oven's real behavior, which matters more than any universal conversion chart once you know it.
Altitude
Above roughly 3,000 feet (900 m), water boils at a lower temperature and moisture evaporates faster, which can dry out baked goods and shift timing further. High-altitude baking often needs a modest temperature increase alongside the standard conversion, plus closer visual checks.
Dish material — glass, ceramic and dark metal
Glass and ceramic bakeware heat more slowly than metal but retain heat longer once hot, which can mean a slightly longer time to start browning followed by faster cooking once the dish itself warms through. When a recipe written for a metal pan is converted to glass, some cooks also lower the oven temperature by about 25°F to avoid overbrowning the exterior before the center catches up.
Applying the Chart to Specific Foods
A chicken breast written for 400°F for 20–25 minutes converts to roughly 375°F for 17–21 minutes on convection — but always confirm with a thermometer at 165°F (74°C) rather than trusting the math alone, since baking a chicken breast is sensitive to thickness in ways a flat percentage cut cannot fully capture. A whole roast chicken converts more conservatively since its center takes longer to catch up regardless of outer air speed.
Converting Times Without a Fixed Percentage Rule
When a dish has no obvious percentage rule — a layered casserole, a dense bread, a custard — the safer approach is to keep the original temperature and simply watch for the same visual and textural cues the recipe describes: a knife coming out clean, a jiggle that has mostly set, an internal temperature reached. Percentage-based time cuts work well for thin, uniform foods and poorly for anything layered or dense.
Two Ovens, One Meal — Splitting the Difference
A common real-world case is baking two dishes that call for different temperatures in one oven at once — say a tray of vegetables written for 425°F alongside a casserole written for 350°F. Picking a middle temperature around 375–400°F usually works: the vegetables need slightly longer than their original time, and the casserole finishes a bit sooner. Check both a few minutes early rather than trusting either original time exactly, since neither dish is baking at its intended setting anymore.
The same logic applies to sheet-pan dinners combining meat and vegetables with different ideal temperatures. Choose the setting closer to what the meat needs for safety, and expect the vegetables to need a short rescue under the broiler at the end if they have not browned enough by the time the meat reaches its safe internal temperature.
Common Mistakes
- Applying the same 25 percent time cut to every dish regardless of thickness leads to underdone centers in dense casseroles even while the surface looks perfectly browned and finished on top.
- Converting Fahrenheit to Celsius by simple subtraction instead of the proper formula introduces errors of ten degrees or more, which compounds across a long bake into a meaningfully different result by the end.
- Ignoring oven calibration and trusting the dial exactly as printed means every conversion inherits that same built-in error, so two ovens set to an identical number can finish minutes apart from each other.
- Switching to convection without lowering the temperature at all can scorch the exterior of delicate items before the interior finishes cooking through to a safe temperature.
- Skipping the thermometer check on converted meat and poultry recipes assumes the math was exact; it rarely is, and safety always depends on the reading, not the formula.
A Quick-Reference Lookup Table
| Written Temp | Nearest 25°F Step Down | Nearest 25°F Step Up |
|---|---|---|
| 325°F | 300°F | 350°F |
| 350°F | 325°F | 375°F |
| 375°F | 350°F | 400°F |
| 400°F | 375°F | 425°F |
| 425°F | 400°F | 450°F |
This lookup is useful when a recipe's exact temperature is not available on your oven's dial, or when you need to bump a dish up or down a single step to share oven space with something else. Moving one 25°F step generally shifts total time by 10–15 percent in the opposite direction — lower and slower, or higher and faster.
Quick Answers
How much do you lower the temperature for a fan oven?
Lower it by about 20–25°F (roughly 10–15°C) from the conventional setting, and start checking doneness 15–20 percent earlier than the original recipe time. Manufacturer guidance varies, so treat this as a starting point rather than an exact rule.
Does converting Fahrenheit to Celsius change cooking time?
No — converting between temperature scales alone does not change time, since 350°F and 177°C describe the same heat. Time only changes when you also switch oven types (conventional to convection) or adjust the actual temperature up or down.
Is there one universal formula for every recipe?
No single formula fits every dish. Thin, uniform foods respond well to percentage-based time cuts; dense, layered, or custard-style dishes are safer left at their original temperature and judged by the same doneness cues the recipe describes.