How roast times scale with weight
Roasting times are not fixed — they scale directly with the weight of the joint or bird. The standard approach is a minutes-per-kilogram rate plus a short base time to account for the initial heat-up. For example, a 2 kg chicken at 45 min/kg plus a 20-minute base requires roughly 110 minutes in a 200°C oven.
A few factors will shift the actual time beyond the estimate:
- Starting temperature — meat straight from the fridge takes longer than meat rested at room temperature for 30–60 minutes before roasting.
- Shape — a compact, thick joint retains heat differently from a long, thin one of the same weight.
- Bone-in vs boneless — bone conducts heat to the centre, so a bone-in joint can cook faster than boneless of the same weight.
- Oven variation — domestic ovens can run 10–20°C hotter or cooler than the dial indicates. An oven thermometer removes the guesswork.
Why a thermometer beats the clock
Timing is a guide — a meat thermometer is the only reliable way to confirm doneness. Insert it into the thickest part of the meat, away from bone or fat. The calculator shows the target internal temperature for each meat and doneness level. Cross-reference with the safe cooking temperatures chart for the full USDA-aligned reference.
The importance of resting
After removing meat from the oven, resting it under a loose tent of foil for 10–20 minutes allows the juices to redistribute through the muscle fibres. A rested joint carves more cleanly and stays moist longer than one cut immediately. The internal temperature also rises slightly during resting — a phenomenon called carry-over cooking — so pull the roast from the oven 2–3°C below your final target if you prefer precision.
Oven temperature and unit conversion
The temperatures above are for a conventional (non-fan) oven. If you are using a fan oven, reduce the temperature by 20°C (roughly 35°F). Not sure how your oven measures up? Use our oven temperature converter to switch between Celsius, Fahrenheit, and gas marks in one tap.
Plan the full meal with Swoodie
Getting the roast right is only part of a great meal. Swoodie helps you discover, save, and coordinate recipes so everyone at the table gets exactly what they want — from the roast to the sides and dessert. Pair the cooking time estimate with the safe cooking temperatures chart to confirm your meat is cooked through, or the oven temperature converter when a recipe uses a scale your oven does not.
These estimates assume a conventional (non-fan) oven pre-heated to the stated temperature. Always verify doneness with a meat thermometer — cooking times are a guide, not a guarantee of food safety.
Frequently asked questions
How long does it take to cook a roast chicken?
A whole chicken roasted at 200°C (390°F) needs approximately 45 minutes per kilogram plus a 20-minute base time. A 1.5 kg chicken takes around 88 minutes; a 2 kg chicken around 110 minutes. Always check that the thickest part of the thigh reaches 74°C (165°F) before serving.
How long should I cook a beef roast per kg?
At 190°C (375°F) in a conventional oven, allow 35 minutes per kg for rare, 45 minutes per kg for medium, or 55 minutes per kg for well done — plus a 20-minute base time for all. A meat thermometer reading of 52°C (125°F), 63°C (145°F), or 71°C (160°F) at the centre confirms the respective doneness.
How long does a turkey take to cook per kg?
Roast a whole turkey at 180°C (355°F) for approximately 40 minutes per kilogram plus a 20-minute base. A 5 kg turkey takes around 220 minutes (3 h 40 min). The internal temperature at the thickest part of the thigh should reach 74°C (165°F). Always rest the turkey for at least 20 minutes before carving.
What temperature should I cook pork to?
Pork should reach an internal temperature of 63°C (145°F) at its thickest point, followed by a 3-minute rest. The calculator uses 180°C (355°F) oven temperature and allows 55 minutes per kg plus a 25-minute base. Colour alone is not a reliable indicator — a thermometer is essential.
How much longer does a joint take from the fridge?
Taking meat straight from the fridge adds roughly 10–15% to the cooking time compared with meat rested at room temperature for 30–60 minutes before roasting. For food safety, do not leave raw meat at room temperature for more than 2 hours. Use the calculator as your starting estimate, then verify with a thermometer.