Estimate elevation gain on a ride.
Elevation gain is best characterised by climbing density — metres of ascent per kilometre of route — because that single figure tells you far more about how hard a ride will feel than total distance does. Flat riding sits around 4 m/km, rolling countryside about 12, hilly terrain 22, and alpine routes 35 or more. The energy cost follows directly from physics: lifting rider and bike through the total ascent is mass times gravity times height, and since a cyclist converts only around 22 percent of metabolic energy into useful work, the calorie cost is roughly four and a half times the mechanical work done.
Elevation gain
Gain m = distance km x climbing density
Climbing energy
kcal = mass kg x 9.81 x gain m / 1000 / (4.184 x 0.22)
Because it is comparable across route lengths. A thousand metres over 30 km is a hard hilly ride; the same thousand over 150 km is barely noticeable. Density immediately places a route on a scale you can feel, which is why route-planning tools all report it.
On climbs, more than anything else. The work to lift mass is directly proportional to that mass, so a 95 kg rider-and-bike does 12 percent more work than an 85 kg one over identical ascent. On the flat, weight barely matters — aerodynamics dominates there instead.