Baking Time Calculator - Roasting Time by Weight & Oven Temp

Your roast weighs 2.3 kg and the recipe only covers 1 kg - now what?

Three problems, one tool. First: meat roasting time scales with weight but not linearly - a 2 kg chicken needs more than double the time of a 1 kg piece because heat penetrates from the outside in. Second: fan ovens run about 20C hotter in practice, so a conventional recipe needs adjustment. Third: Gas Mark 6 means nothing to someone with a Celsius dial. This calculator handles all three scenarios with per-cut timing data for 8 types of meat, automatic fan/conventional conversion, and a full C/F/Gas Mark table.

How to use this calculator - step by step

Select mode - meat roasting (time by weight), baking adjustment (fan vs conventional), or temperature converter (C/F/Gas Mark).
Meat mode: pick the cut, enter raw weight in grams, select your oven type, and (for beef) choose doneness. The calculator returns total cooking time and recommended temperature.
Baking mode: select the type of bake, enter the recipe temperature, and tell the calculator what the recipe assumes vs what you have. It adjusts both temperature and time.
Converter mode: enter any temperature in C, F or Gas Mark and get all three equivalents plus a heat-level description.
Read the results - cooking time, oven temperature, and practical tips specific to your cut or bake type.

Meat roasting times - reference table

Base times per 500 g of raw weight, conventional oven. Fan oven: subtract 20C and reduce time by 15%.

Cut	Temp (C)	Min per 500g	Base extra	Internal temp
Whole chicken	200	20	+20 min	75-80C
Beef roast (medium)	180	20	+20 min	60-65C
Pork loin	180	30	+30 min	70-75C
Whole turkey	180	20	+30 min	80C
Pork shoulder	170	35	+20 min	70-75C
Lamb leg	180	20	+20 min	65-75C

Practical examples

Example 1: Whole chicken, 1.8 kg, conventional oven
Result: 1 hr 32 min at 200C (20 min/500g x 3.6 + 20 min base = 92 min)

Example 2: Beef roast, 2.5 kg, fan oven, medium doneness
Result: 1 hr 36 min at 160C (fan adjustment: -20C, -15% time)

Example 3: Recipe says 180C conventional, you have fan oven
Result: Set to 160C fan, reduce baking time by 15%

Example 4: Convert Gas Mark 6 to Celsius and Fahrenheit
Result: 200C / 392F - high heat (pizza, roasts)

Example 5: Turkey, 5 kg, conventional oven
Result: 3 hr 30 min at 180C (20 min/500g x 10 + 30 min = 230 min)

FAQ - Frequently asked questions

Why is fan oven 20C lower than conventional?

Fan (convection) ovens circulate hot air actively, which transfers heat to food more efficiently. The moving air eliminates cold spots and creates a more uniform temperature. In practice, this means food cooks as if it were 20C hotter, so you reduce the dial by 20C to get the same result. Time drops by about 15% as well.

Should I trust the calculated time or use a meat thermometer?

Always use an internal meat thermometer for the final call. The calculated time is a reliable estimate based on weight and cut, but every oven has hotspots and every piece of meat has a slightly different shape. The thermometer gives you certainty. Target temperatures: chicken 75C, pork 72C, beef rare 55C, medium 63C, well done 72C.

Does the calculator account for bone-in vs boneless?

The times assume typical cuts (bone-in for whole poultry, boneless for breast/loin). Bone-in roasts take 5-10 min longer per 500g because bone slows heat transfer. If you have a bone-in beef roast, add about 10% to the calculated time and verify with a thermometer.

What is Gas Mark and where is it used?

Gas Mark is a temperature scale used primarily in the UK and Ireland for gas ovens. It runs from 1 (140C/284F) to 9 (240C/464F). Most British recipes from cookbooks and BBC Good Food use Gas Mark alongside Celsius. If your oven has a C or F dial, just use the converter mode.

Why does resting meat after cooking matter?

When meat cooks, juices move toward the center (away from the heat). If you cut immediately, the juices run out onto the board. Resting for 10-15 minutes allows juices to redistribute throughout the meat, resulting in a moister, more flavorful slice. Cover loosely with foil - the internal temperature will continue rising by 3-5C (carryover cooking).

Can I use this for frozen meat?

No. The calculator assumes room-temperature meat (taken out of the fridge 30-60 min before cooking). Cooking from frozen adds 50-100% more time and is not recommended for large cuts because the outside overcooks before the center thaws. Always thaw meat fully before roasting. Exception: small cuts like chicken breast can go from fridge (not freezer) to oven with only a few extra minutes.

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