Climb Difficulty Calculator (FIETS Index)

It uses the FIETS index from Dutch cycling magazine Fiets: score = ascent² ÷ (length × 10), with both ascent and length in metres, plus an altitude bonus of (summit − 1000) ÷ 1000 when the climb tops out above 1000 m. Squaring the ascent means a short, steep climb scores far higher than a long, gentle one of the same total gain.

The standard FIETS bands match Tour de France categories: Cat 5 ≥ 0.25, Cat 4 ≥ 0.5, Cat 3 ≥ 2.0, Cat 2 ≥ 3.5, Cat 1 ≥ 5.0 and HC (Hors Catégorie) ≥ 6.5. For example, Alpe d'Huez (1096 m of ascent over 13.8 km, summit 1850 m) scores 1096² ÷ (13800 × 10) + 850 ÷ 1000 ≈ 8.7 + 0.85 ≈ 9.6, comfortably HC.

FIETS divides ascent² by climb length, so it only makes sense for one continuous climb. On a mixed route with descents and flats the total ascent and total distance do not describe a single gradient, so the score is meaningless. For a multi-climb day, score each major climb separately.

Only summit altitude is included, via the altitude bonus. Rough surface, headwind, heat and thin air near the top can all make a climb feel harder than the FIETS score alone suggests.