Roasting meat isn’t guesswork—it’s arithmetic. Whether you’re preparing a ribeye roast for a holiday dinner or a whole chicken on a Sunday afternoon, knowing how long it needs to stay in the oven depends largely on one variable: weight. The cooking method, internal temperature goal, and oven settings all matter—but it starts with the scale.
This article outlines how to calculate roasting times by weight across different meats. It includes standard time-per-weight formulas, temperature targets, and signs your roast is done—without relying only on timers.
Why Weight Matters More Than Appearance
A 1.5 kg roast might look similar to a 2.5 kg one in shape, but the difference in mass significantly affects heat penetration. Larger cuts retain more internal moisture and take longer to reach safe internal temperatures. Calculating cooking time per 500 grams or per pound gives you a controlled and repeatable method that’s more precise than relying on visual cues.
General Time-Per-Weight Guidelines
Cooking times vary based on meat type, whether it’s bone-in or boneless, and your desired doneness level. Use these benchmarks as starting points.
Beef Roasts (Ribeye, Sirloin, Rump)
- Rare: 15 minutes per 500g at 220°C
- Medium: 20 minutes per 500g at 200°C
- Well done: 25 minutes per 500g at 180°C
Lamb Roasts
- Medium-Rare: 20 minutes per 500g at 200°C
- Medium-Well: 25 minutes per 500g at 190°C
- Well done: 30 minutes per 500g at 180°C
Pork Roasts (Shoulder, Loin)
- 30–35 minutes per 500g at 180°C
Pork needs to be fully cooked. Always confirm with a thermometer.
Chicken (Whole)
- 45 minutes per kg at 180°C
Whole poultry requires higher vigilance. Undercooked chicken poses health risks.
Turkey
- 40–45 minutes per kg at 170°C
Larger birds take longer, especially when stuffed.
How to Calculate It Yourself
Use a simple formula based on the weight and target cooking time per 500 grams (or per kilogram):
Total time (in minutes) = (Weight in grams / 500) × time per 500g
For example:
- A 1.5 kg beef roast for medium doneness:
(1500 / 500) × 20 = 60 minutes - A 2.2 kg whole chicken:
(2200 / 1000) × 45 = 99 minutes (or 1 hour and 39 minutes)
If you want a shortcut, a cooking time calculator can automate this process with presets for meat types and doneness preferences.
Doneness Isn’t Just About Time
Weight-based estimates help get close, but they’re never final. Meat reacts differently depending on fat content, bone density, and even your oven’s quirks. That’s where internal temperature readings step in.
Target Internal Temperatures
Use a meat thermometer for these readings at the thickest part, avoiding bone.
- Beef (Rare): 50°C
- Beef (Medium): 60°C
- Beef (Well done): 70°C
- Lamb: 60–75°C
- Pork: 70°C
- Chicken: 75°C (including juices running clear)
- Turkey: 75°C (thigh and breast)
Resting Time Matters Too
Don’t carve immediately after cooking. Let the roast rest uncovered for at least 10–20 minutes depending on size. During this time:
- Juices redistribute, reducing dryness
- Internal temperature can rise by 3–5°C
- Texture becomes more uniform
Resting should always be factored into your schedule. The roast may finish cooking internally while resting, particularly for beef and lamb.
Adjustments Based on Oven and Cut
Not all ovens are calibrated the same. Fan-assisted ovens tend to cook faster, so consider reducing temperature by 10–15°C or shortening the cook time by 5 minutes per 500g.
Also, bone-in roasts cook a bit faster due to heat conduction through the bone. Boneless versions, being denser, often need a touch more time. Add 5 extra minutes per 500g to boneless cuts if unsure.
Quick Reference: Weight-to-Time Cheat Sheet
| Meat Type | Weight | Doneness | Time (approx.) |
|---|---|---|---|
| Beef (Ribeye) | 1.2 kg | Medium | 48 mins |
| Lamb Leg | 2.0 kg | Medium-Well | 100 mins |
| Pork Loin | 1.5 kg | Full Cooked | 105 mins |
| Whole Chicken | 1.8 kg | Fully Cooked | 81 mins |
| Turkey | 4.0 kg | Fully Cooked | 180 mins |
Summary Tips
- Weigh your roast precisely before calculating
- Use the time-per-500g rule to plan the main roast duration
- Always check internal temperature before serving
- Factor in 10–20 minutes of resting after cooking
- Use a thermometer instead of relying solely on time
- Use bone-in cuts for faster cooking and richer flavor
- For added ease, try a cooking time calculator to save prep time
Calculating cooking time by weight gives structure to your roasting routine. Whether you’re preparing a feast or just dinner for two, letting the math guide the heat is the difference between dry disappointment and succulent satisfaction.