How is climb difficulty scored?

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.

What FIETS score is each category?

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.

Why is this for a single climb and not a whole route?

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.

Does this account for road surface, altitude air or weather?

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.

BikeCalcs

Climb Difficulty Calculator (FIETS Index)

Score a single continuous climb using the FIETS index from its length, ascent and summit height.

Climb Length

Length of the single continuous climb (km)

Total Elevation Gain

Total metres of ascent from foot to summit of this climb

Summit Elevation

Height above sea level at the top — adds an altitude bonus above 1000 m

How We Calculate This

FIETS Index Scoring

Base Score = Ascent² / (Length × 10), with ascent and length both in metres
Altitude Bonus = (Summit Elevation − 1000) / 1000, added only when the summit is above 1000 m
FIETS Score = Base Score + Altitude Bonus
Category: Cat 5 ≥ 0.25, Cat 4 ≥ 0.5, Cat 3 ≥ 2.0, Cat 2 ≥ 3.5, Cat 1 ≥ 5.0, HC ≥ 6.5

Frequently Asked Questions

Related Calculators

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Elevation Gain Calculator

Calculate total elevation gain from gradient and distance.

Ascent Time Calculator

Estimate climbing time from power, weight and gradient.

Descent Speed Calculator

Estimate safe descent speed based on gradient and conditions.

Last updated: June 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.