A free rucking calorie calculator that estimates the energy cost of walking with a loaded pack using the Pandolf load-carriage equation with Drain et al.'s modern correction factor — the same math used by US Army planners. Enter your bodyweight, pack weight, pace, grade, and terrain factor; the tool returns watts and kcal/min, plus a MET-only comparison so you can see how much extra burn the load actually adds. Every formula and assumption is shown on the page, and the underlying engine is the same one powering the CalBurndown mobile app.