Calories burned carrying a loaded pack ā computed with the Pandolf equation, the US Army's validated load-carriage formula, not a generic MET guess.
For a 180 lb person on gravel or light-brush terrain at zero grade, here's what the Pandolf equation predicts per hour:
| Ruck Weight | 3.0 mph | 3.5 mph | 4.0 mph |
|---|---|---|---|
| 20 lb | ~360 kcal | ~450 kcal | ~555 kcal |
| 35 lb | ~385 kcal | ~480 kcal | ~595 kcal |
| 50 lb | ~410 kcal | ~515 kcal | ~635 kcal |
Add hills and the numbers climb fast ā a 5% average grade raises the hourly burn by roughly 55-60% at the same speed and load.
Developed by K.B. Pandolf and colleagues at the US Army Research Institute of Environmental Medicine in 1977, the equation predicts metabolic rate in watts: M = 1.5W + 2.0(W+L)(L/W)Ā² + Ī·(W+L)(1.5VĀ² + 0.35VG), where W is bodyweight (kg), L is load (kg), V is speed (m/s), G is grade (%), and Ī· is a terrain factor from 1.0 (paved) to 2.1 (loose sand). Watts convert to calories at roughly 0.86 kcal per hour per watt.
It remains the standard load-carriage model used in military planning. Recent validation research suggests it can under-predict by 10-30% at very heavy modern military loads and unusual speeds, but for recreational rucking ā 15 to 50 lb at 2.5 to 4.5 mph ā it typically lands within about 5-10% of laboratory-measured energy cost, which is far better than generic MET tables that ignore load entirely.
If you're training for a timed ruck standard, calorie burn is only half the picture ā pacing matters more. A 12-mile ruck at 15:00/mile pace with 35 lb burns in the neighborhood of 1,800 kcal for a 180 lb soldier on easy terrain ā more with hills. Pair this tool with our ACFT Score Calculator, USMC PFT Calculator, or Navy PRT Calculator for test prep and our Steps to Miles Calculator to track weekly mileage.
Per minute, running usually burns more. Per session, rucking often wins because you can sustain it far longer at lower injury risk ā an hour of rucking with 35 lb burns roughly what 35-40 minutes of easy running does, with much less impact. They're complementary, not competing.
Most coaches recommend starting at about 10% of bodyweight and progressing toward 20-30% over several months. Our rucking for beginners guide lays out a full 8-week progression. Jumping straight to 50 lb is the most common cause of rucking overuse injuries ā the calorie difference doesn't justify the risk early on.
Most watches estimate calories from heart rate and treat your ruck as a regular walk ā they don't know about the pack. Heart-rate-based estimates also drift with heat, caffeine, and fatigue. The Pandolf equation models the actual mechanical work of carrying load, which is why militaries use it.
Yes, with a caveat. A vest carries closer to your center of mass than a backpack, which lowers the true cost slightly ā expect the real number to be a few percent under the prediction. It's still far more accurate than ignoring the load.