The formula we use
The primary calculation is the Pandolf equation for loaded walking. It predicts metabolic rate in watts:
M = 1.5W + 2.0(W + L)(L / W)^2 + eta(W + L)(1.5V^2 + 0.35VG)| Variable | Meaning | Our input |
|---|---|---|
| M | Metabolic rate in watts | Calculated |
| W | Body mass in kilograms | Body weight |
| L | External load in kilograms | Ruck weight |
| V | Walking speed in meters per second | Pace |
| G | Grade as a percent | 0-15% uphill grade |
| eta | Terrain coefficient | Paved, gravel, trail, or sand |
Implementation details
- Body weight and ruck weight are converted from pounds to kilograms when imperial units are used.
- Pace is converted from minutes per mile into meters per second.
- Grade is clamped between 0% and 15%. The current tool models flat and uphill rucking, not downhill cost.
- Terrain uses eta values of 1.0 for pavement, 1.2 for gravel or packed dirt, 1.5 for trail, and 2.1 for sand.
- Watts are converted to kcal/hour using the standard approximation of 1 watt = 0.86 kcal/hour.
- Total calories are calculated from either the entered duration or the duration implied by distance and pace.
Why this beats a generic walking calculator
A normal walking calculator usually knows body weight and speed. It usually does not know pack weight, terrain coefficient, or grade. Those are the variables that make rucking different from walking. A 30 lb pack on flat pavement is a different session from the same person carrying the same pack uphill on sand.
Fitness watches are useful for trend tracking, but most do not directly model external load. That means they can underestimate the cost of loaded walking or confuse a ruck with an ordinary walk unless you manually adjust the activity context.
Where the estimate can be wrong
This calculator is intentionally transparent about its limits:
- Individual metabolic efficiency, body composition, and fitness can move real calorie burn above or below the estimate.
- Very light rucks may be overestimated because the equation was developed for military load-carriage contexts.
- Downhill terrain, wind, heat, altitude, mud, route interruptions, and technical footing are not fully modeled.
- The comparison table uses MET values only for non-rucking activities. The rucking number still comes from the Pandolf equation.
How to use the number
Use the estimate to compare sessions and plan weekly training load. Do not treat it as a precise license to eat back calories. For fat loss, the useful pattern is consistency: similar route, similar load, similar pace, and a conservative nutrition plan.