How long do I roast a joint per kilo?

A per-kilo figure is an average derived from typical joints in a typical oven. The reason it so often disappoints is that it treats weight as the variable, when the thing that actually governs cooking time is how far the heat has to travel to the centre — which is thickness, not weight.

Step by step

1. Use the chart to plan, not to decide.A typical set of starting estimates at 180°C, after an initial 20 minutes at 220°C: beef roughly 20 minutes per kilo for rare, 25 for medium, 30 plus for well done. Lamb similar. Pork loin around 30–35 minutes per kilo. A whole chicken around 40–45 minutes per kilo. Add roughly 20 minutes overall to each. Treat every one of those as an estimate with a wide error bar.
2. Correct for shape before you trust the number.A long thin rolled joint of 2kg cooks far faster than a fat compact 2kg one. Bone-in cooks slightly differently again. If your joint is unusually thick, add time; if it is flat or butterflied, take a lot off and start checking early.
3. Correct for your oven.Domestic ovens routinely run 10–20°C away from the dial and fan ovens differ again. If you have never checked yours with an oven thermometer, the per-kilo figure is being applied to a temperature you do not actually know. That is the largest single source of error in roast timing.
4. Set your target internal temperature first.Decide what you are aiming for and work back. Beef and lamb: about 52–54°C rare, 57–60°C pink, 65–68°C well done. Whole-muscle pork: about 63°C. Poultry: cooked thoroughly throughout, around 74–75°C at the thickest part of the thigh. Rolled or stuffed joints: cooked through. Those are the real destinations.
5. Start probing well before the chart says it is ready.Check at about two-thirds of the estimated time, then every fifteen to twenty minutes. A leave-in probe removes the guesswork entirely and stops you opening the oven. Being early is recoverable; being late is not.
6. Subtract carryover from your target.Meat keeps cooking after it leaves the oven — roughly 2–3°C for a small joint, 5–7°C for a large one, more for a very big turkey. Take it out below the target temperature, not at it. This is why timing charts overshoot even when the arithmetic is right.
7. Build the rest into the plan.A joint needs 20–30 minutes resting, and a large one can rest for 45 minutes without going cold. That is not lost time — it is the window in which the potatoes finish and the gravy gets made. Work backwards from serving time through the rest, not forwards from when you put it in.

Tips

• If you are cooking two joints together, the oven has more mass to heat and each joint may take slightly longer than it would alone — but they do not add together. Time each by its own thickness and probe both.
• A joint that finishes early is easy to hold: rest it, then keep it loosely covered somewhere warm, or return it to a 60–70°C oven. A joint that is late holds up the whole meal.
• Turn the joint round halfway through if your oven has a hot corner. Most do.
• For slow-roasting to pull-apart, per-kilo charts do not apply at all — you are aiming for 90–95°C internal and the time is governed by collagen conversion, not by reaching a temperature.

Common mistakes

• Applying a beef chart to a rolled and stuffed joint — Stuffing is dense and slow to heat, and the rolled surfaces are now inside. It needs longer and it needs to be cooked through, not rare.
• Weighing the joint after stuffing it — The chart is for meat. Including the stuffing weight inflates the time for the meat while still not guaranteeing the stuffing is safe.
• Trusting the oven dial — An oven 15°C low turns a two-hour roast into a two-and-a-half-hour one, and the chart cannot know that. An oven thermometer costs very little and fixes it permanently.

Questions people ask