Roast Cooking Time Calculator

How to use this calculator

1. Weigh the joint as it goes inIncluding any stuffing, which adds weight and slows the heat reaching the centre. Weigh a stuffed bird after stuffing it, not before.
2. Tick fan if your oven has oneA fan oven runs effectively hotter than the dial. The calculator converts to the conventional equivalent so the timing works.
3. Enter a serving timeIt works backwards through the resting period to tell you when the joint goes in and when it comes out.
4. Buy a meat thermometerIt costs a few pounds and removes the guesswork entirely. Every timing here is a plan; the temperature is the answer.

Time gets it in the oven; temperature gets it out

Every traditional roasting rule works from weight: so many minutes per pound or per 500 grams, plus a flat addition. Those rules are useful and they are approximations.

The flat addition exists because a joint does not heat instantly. Part of the cooking time is simply bringing the mass up to temperature, and that portion does not scale linearly with weight — which is why doubling the weight does not double the time.

What the weight rule cannot capture is shape. A long thin joint has far more surface area relative to its mass than a thick compact one, so it cooks considerably faster at the same weight. A rolled joint is slower still, because the heat has to travel further to reach the middle.

Starting temperature matters too. A joint straight from the fridge takes noticeably longer than one that has stood out for half an hour, and the outside overcooks while the centre catches up.

And ovens vary. A domestic oven can be 20°C or more away from its dial, which is enough to make every published timing wrong in that kitchen. An oven thermometer costs very little and explains a great deal of inconsistent cooking.

All of which is why the core temperature is the real test. It is a direct measurement of the thing you actually care about, and it is immune to shape, starting temperature and oven calibration.

For beef and lamb, roughly 52°C is rare, 60°C medium and 70°C well done. For pork the target is 71°C, and for poultry 74°C.

Carryover cooking means the temperature keeps rising after the joint comes out — by several degrees on a large joint. So take it out about 3°C below target rather than at it.

Resting is not an optional refinement. During cooking the juices are driven toward the centre, and resting lets them redistribute. Carving immediately loses them onto the board, and the meat is measurably drier for it. Cover loosely with foil; wrapping tightly steams a crisp crust soft.

Worked example: a 1.5 kg sirloin for 1 pm

A 1.5 kg beef sirloin, medium, at 180°C conventional.

At 25 minutes per 500 g, that is 3 × 25 = 75 minutes, plus the flat 20 minutes, giving 95 minutes — one hour and 35 minutes.

Resting for a joint this size is about 22 minutes, so the calculator suggests that by default.

Working back from a 1 pm serving time: the joint comes out of the oven at 12:38 and goes in at 11:23.

That backward calculation is the part people get wrong on a Sunday, because the resting period is easy to forget until the potatoes are ready and the beef is not.

Target core temperature for medium beef is 60°C, and you take it out at about 57°C to allow for carryover.

Now change the oven. At 200°C the same joint needs 95 × (180 ÷ 200) = 85 minutes. At 160°C it needs 107 minutes. Higher temperature is faster but gives a wider band of overcooked meat below the crust; lower and slower gives a more even result.

Now tick fan. A fan oven set to 180°C behaves roughly like a conventional oven at 200°C, so the calculator treats it accordingly and the time comes down to about 85 minutes. Setting a fan oven to the conventional temperature in a recipe is the single most common cause of a joint being done twenty minutes early.

Now a different joint. The same 1.5 kg as pork loin needs 30 minutes per 500 g plus 30 — 120 minutes — and must reach 71°C rather than 60. Pork is not served pink, and the extra time reflects that.

A 1.5 kg gammon needs 20 per 500 g plus 20, or 80 minutes, to reach 68°C.

And a 5 kg turkey needs 20 per 500 g plus a much larger flat addition of 70 minutes — 270 minutes, or four and a half hours — because a large bird takes a long time simply to warm through before any cooking happens.

Across all of those, the timing puts it in the oven and the thermometer takes it out.

Timings and target temperatures

The core temperature column is the one to trust. Pork, gammon and poultry must be cooked through — Food Standards Agency guidance is 75°C for two minutes or an equivalent time and temperature combination, which is a food safety requirement rather than a matter of preference. Beef and lamb can be served pink because contamination is on the surface and is killed by searing; minced or rolled joints are different, because the surface has been folded inside.

Getting it right on the day

Take the joint out of the fridge thirty to sixty minutes before it goes in the oven. A cold centre is the commonest reason a joint takes longer than the timing says.

Sear if you want a crust. Twenty minutes at 220°C at the start, then down to the roasting temperature, develops colour and flavour through the Maillard reaction. The calculator adds searing time on top rather than including it in the main figure.

Position matters. A joint on a rack lets air circulate underneath and roasts evenly; one sitting in its own fat effectively fries on the bottom. A rack also keeps it clear of the liquid if you are making gravy in the tin.

Do not open the oven more than necessary. Each opening drops the temperature substantially and adds time, and the effect is worse in a fan oven where the recovery involves the fan pushing cold air over the food.

For a large bird, cover the breast with foil for the first two thirds and remove it to brown. Breast meat reaches temperature well before the thigh, and that is why turkey so often ends up dry — the timing is set by the slowest part.

Check the temperature in the thickest part, away from bone. Bone conducts heat and gives a falsely high reading, and a probe touching it will tell you the joint is done when it is not.

On resting: fifteen minutes for a small joint, up to forty-five for a large one, and a big turkey benefits from a full hour. The joint stays hot far longer than people expect — the loss over thirty minutes under foil is modest, and the improvement in texture is not.

Use the resting time. It is when the roast potatoes crisp, the Yorkshire puddings go in and the gravy gets made, and planning around it turns a stressful hour into a manageable one.

On leftovers: cool within two hours, refrigerate, and reheat only once until piping hot throughout. Cooked meat keeps three to four days refrigerated.

A note on gammon specifically. Many joints are cured and benefit from soaking or simmering before roasting to reduce saltiness — check whether yours is marked as requiring it, because a joint that needed soaking and did not get it is unpleasantly salty and there is no fixing it afterwards.

And finally, ovens. If timings never seem to work in your kitchen, buy an oven thermometer before blaming the recipe. A dial reading 180°C in an oven actually running at 160°C makes every published time wrong by a quarter.

Assumptions and limitations

• Weight-based timings are approximations, not precise rules
• Does not account for joint shape, which affects cooking time substantially
• Assumes the joint starts at room temperature rather than fridge cold
• Assumes the oven runs at the temperature on its dial, which many do not
• Bone-in joints and stuffed birds cook differently from the figures shown
• Does not cover slow roasting, pot roasting or covered cooking
• Core temperature is the reliable test — use a thermometer

Questions people ask about this in United Kingdom