Climb categories explained: Cat 4 to Hors Catégorie

Every cycling climb category — from a modest Cat 4 to an Hors Catégorie monster — comes from one simple number: length times grade. Here's exactly how it's calculated, the real thresholds, and how a route analyzer decides where a climb even starts and ends.

What "Cat 4" through "HC" actually mean

Climb categories originated with the Tour de France, ranking climbs from easiest to hardest: Category 4 is the mildest categorized climb, Category 1 is serious, and Hors Catégorie ("beyond category") is reserved for the biggest mountain passes — the ones a numbered category couldn't do justice to. GPS route-planning and ride-tracking platforms borrowed the same five-tier scale so riders could tell, at a glance, how hard a climb on their route is before they get there.

The score: length × grade

The category isn't a judgment call — it comes from one formula, used the same way by RideWithGPS, GPSLogger and Strava:

score = length (m) × average grade (%)

That's equivalent to roughly elevation gain (m) × 100. A 5 km climb averaging 8% scores 5,000 × 8 = 40,000. A short, brutal 800 m ramp at 12% scores 800 × 12 = 9,600 — shorter, but still enough to qualify.

The category boundaries

A climb's score maps onto the five categories using the thresholds below — the RideWithGPS/GPSLogger convention, which is more generous at the top end than Strava's stricter cutoffs for Cat 1 and HC:

A detected climb scoring 8,000 or under isn't discarded — it just doesn't clear the bottom rung, so it shows as "uncategorized" rather than as one of the five named categories. That's useful on rolling terrain that has real short rises without a single Tour-scale climb.

How a climb is actually found in GPS data

Before any of the above can run, something has to decide where a climb starts and ends in a stream of elevation points. That happens in three steps:

• Ascending runs. The route is scanned for stretches where the point-to-point grade, measured on smoothed elevation, stays at or above 3% — the minimum grade a climb needs to even begin.
• Merging across dips. Real climbs aren't a single unbroken ramp — they have short flat sections and dips. Neighbouring ascending runs get merged into one climb as long as two conditions both hold: the merged section's overall average grade stays at or above 3%, and the descent inside the merged section stays under half of its total climbing. That second rule stops a real descent between two separate hills from being counted as one climb.
• Qualifying. A merged stretch only counts as a climb once it clears three floors together: at least 500 m long, averaging at least 3% grade, and a score of at least 1,500. Anything short of that is rolling terrain, not a climb.

Sources

Score formula and category thresholds: RideWithGPS, GPSLogger, Strava. Climb-detection minimums (500 m, 3% grade, score ≥ 1,500) and the 3%-merged-average rule: Garmin ClimbPro. Descent-under-half-of-gain merge rule: GPSLogger.