The most reliable way to calculate calories burned lifting weights is with the MET formula: multiply 0.0175 by the MET value of your activity, then by your body weight in kilograms, then by the number of minutes you exercised. A 180-pound person lifting weights at moderate intensity for 45 minutes burns roughly 225 calories during the session, though the real total is higher once you factor in what your body burns recovering afterward.
The MET Formula, Step by Step
MET stands for metabolic equivalent of task. It’s a standardized way of expressing how hard an activity works your body compared to sitting still, which counts as 1 MET. General weightlifting falls between 3 and 6 METs depending on how intensely you train. Light effort with long rest periods sits around 3.0 METs. Moderate-intensity lifting (think typical hypertrophy training with 60 to 90 seconds of rest between sets) lands near 3.5 to 5.0 METs. Circuit training or supersets with minimal rest can push above 6.0.
The formula, developed from exercise physiology research at the University of Colorado, works like this:
- Calories per minute = 0.0175 × MET value × your weight in kilograms
- Total calories = calories per minute × total minutes of exercise
To convert pounds to kilograms, divide by 2.2. So for a 180-pound (81.8 kg) person doing moderate lifting at 3.5 METs:
0.0175 × 3.5 × 81.8 = 5.01 calories per minute. Over a 45-minute session, that’s about 225 calories.
A heavier person burns more calories doing the exact same workout because it takes more energy to move and support a larger body. A 140-pound person doing that same session would burn closer to 175 calories, while someone at 220 pounds would clear 275.
Why the MET Number You Choose Matters
The biggest variable in this calculation isn’t your weight or duration. It’s picking the right MET value, which depends on how you actually train. A session where you do three sets of bicep curls, check your phone for two minutes, then do three sets of lateral raises is genuinely different from a session where you’re squatting heavy with short rest periods and sweating through your shirt.
Here’s a rough guide:
- Light effort (MET 3.0): Machine-based exercises, long rest periods, low sets
- Moderate effort (MET 3.5–5.0): Free weights, compound lifts, 60–90 second rest periods
- Vigorous effort (MET 5.0–6.0): Supersets, circuit training, minimal rest, high volume
Most people doing a standard gym session with a mix of compound and isolation exercises fall in the 3.5 to 5.0 range. If you’re unsure, 3.5 is a conservative and realistic estimate for a typical hour of lifting.
The Afterburn Effect Adds 50 to 127 Calories
The MET formula only captures what you burn during the workout itself. After you finish lifting, your body continues consuming extra oxygen to repair muscle tissue, clear metabolic byproducts, and restore energy reserves. This elevated calorie burn is called excess post-exercise oxygen consumption, or EPOC.
Research compiled at the University of New Mexico found that EPOC from resistance training adds roughly 51 to 127 extra calories on top of the workout itself. That afterburn stays elevated for at least three hours post-exercise, with some studies measuring it even longer after particularly intense sessions. The higher end of that range comes from workouts with shorter rest periods and higher overall volume, while lighter sessions produce less afterburn.
So that 225-calorie moderate lifting session for a 180-pound person likely costs the body closer to 275 to 350 total calories once recovery is included. It’s not a dramatic number, but it’s a meaningful addition that most online calculators ignore entirely.
How Accurate Are Fitness Trackers?
If you rely on an Apple Watch, Fitbit, or similar device for calorie tracking, expect significant error during weight training. A 2025 study from the University of Mississippi found that wearable devices had an average error of nearly 28% for energy expenditure, far worse than their accuracy for heart rate (about 4.4% error) or step counts (about 8% error). That inaccuracy held across all activity types and user profiles tested.
The core problem is that most wearables estimate calorie burn primarily through heart rate, and heart rate doesn’t map cleanly onto energy expenditure during resistance training. Your heart rate spikes during a heavy set of deadlifts and drops during rest, but the actual metabolic cost of repairing the muscular damage and handling the load isn’t fully captured by those fluctuations. Lifting also involves significant anaerobic energy production, which heart rate monitors weren’t designed to track.
In practical terms, if your watch says you burned 300 calories lifting, the real number could be anywhere from 215 to 385. That’s a wide enough range to meaningfully throw off anyone trying to manage their calorie intake with precision. Using the MET formula with an honest assessment of your intensity will typically get you closer to the truth than your wrist will.
Factors That Shift Your Calorie Burn
Beyond body weight and workout intensity, several other variables influence how many calories a lifting session actually costs you.
Muscle mass: Muscle tissue burns roughly 4.5 to 7 calories per pound per day at rest, according to metabolic research. That’s not the dramatic “muscle burns 50 calories per pound” claim you’ll see in fitness marketing, but it does mean that two people at the same body weight will burn different amounts during the same workout if one carries significantly more muscle. The person with more lean mass has a higher baseline metabolic rate and tends to burn slightly more during exercise as well.
Exercise selection: Compound movements like squats, deadlifts, bench presses, and rows recruit large muscle groups across multiple joints. They demand more total energy per rep than isolation exercises like curls or calf raises. A workout built around big compound lifts will burn meaningfully more than one focused on smaller, single-joint movements, even at the same duration and perceived effort.
Rest periods: Shorter rest periods keep your heart rate elevated and increase the metabolic demand of the session. Cutting rest from two minutes to 60 seconds between sets can shift you from a 3.5 MET effort to closer to 5.0, which represents a roughly 40% increase in calories per minute.
Training experience: Beginners tend to be less efficient at recruiting muscle fibers and often use more energy performing the same movement than experienced lifters. However, experienced lifters typically handle heavier loads and higher volumes, which offsets that difference. The net result is that training experience alone doesn’t change the calorie equation dramatically in either direction.
A Realistic Calculation Example
Here’s what a full calculation looks like for a common scenario. Say you weigh 160 pounds (72.7 kg), you train for 50 minutes doing a mix of barbell and dumbbell exercises with about 90 seconds of rest between sets, and you’d rate your effort as moderate.
A MET value of 4.0 is reasonable for that kind of session.
0.0175 × 4.0 × 72.7 = 5.09 calories per minute.
5.09 × 50 minutes = 254 calories during the workout.
Add 50 to 100 calories for the afterburn effect.
Total estimated expenditure: 304 to 354 calories.
That’s a solid estimate for planning purposes. If you’re using this number to adjust your food intake, rounding to the lower end (around 300 calories) gives you a buffer against overestimating. The MET formula isn’t perfect, but paired with an honest assessment of your effort level and a conservative afterburn estimate, it’s the most practical tool available outside of a metabolic lab.