Cycling
10 calculators
Cycling calculators built around power rather than speed. Power in watts is the one measure that does not change with wind, gradient or draft, which is why training targets, testing protocols and load tracking are all built on it.
The tools here cover the four things a power figure feeds: a threshold estimate, the zones derived from it, the training load a session accumulates, and the mechanical figures — gearing, chain length, spoke length — that decide what the bike itself can do.
- Cycling Power Calculator (Watts from Speed) Estimate cycling power from speed, mass, drag area, rolling resistance, and gradient.
- Cycling Power Zones Calculator Calculate Coggan seven-zone power training ranges from your Functional Threshold Power (FTP).
- FTP Calculator (from 20-Min Test) Estimate Functional Threshold Power by applying a 0.95 factor to your 20-minute test result.
- Power-to-Weight Ratio Calculator Calculate watts per kilogram and compare against duration-specific performance bands
- Training Stress Score (TSS) Calculator Calculate Training Stress Score from workout duration, Normalized Power, and FTP.
- Bike Gear Ratio Calculator Calculate gear inches from chainring, rear cog, and wheel diameter to compare drivetrain ratios.
- Climbing Watts Calculator Estimate climbing power from VAM and total mass using gravitational work principles.
- Cycling Pace Converter (MPH to km/h) Convert cycling speeds between miles per hour and kilometers per hour instantly
- Chain Length Calculator Calculate optimal chain length for single-speed and track bikes using chainring, cog, and chainstay measurements.
- Spoke Length Calculator Calculate radial spoke length from rim ERD, flange radius, and spoke hole count.
FTP, zones and training load
Functional threshold power is conventionally estimated as 95% of the average power held over a 20-minute maximal effort. The 5% discount exists because a 20-minute effort sits above the intensity a rider could hold for an hour, which is what the threshold is meant to represent. Power zones are then expressed as percentages of that figure, so an FTP that is wrong by 10 watts moves every zone boundary with it.
Training Stress Score combines duration and intensity into one number, scaled so that an hour at exactly threshold scores 100. That scaling is what makes a 90-minute endurance ride and a 40-minute interval session comparable at all, and it is also why the score is meaningless if the FTP behind it is stale.
Power-to-weight in watts per kilogram is the figure that governs climbing, because gravity scales with mass while air resistance largely does not. On flat ground absolute watts matter more, which is why the same two riders can swap places depending on the terrain.
The mechanical calculators
Gear ratio divides chainring teeth by sprocket teeth, and gear inches multiply that ratio by the wheel diameter to give a figure comparable across bikes with different wheel sizes. Chain length and spoke length are geometric rather than physiological: chain length follows from chainstay length and the two largest rings, and spoke length from hub flange geometry, rim diameter and the lacing pattern.
These are the calculations where an error is expensive rather than merely inaccurate. A spoke two millimetres short does not tension properly, and a chain a link short cannot be shifted into the largest combination without damage.
Common questions
Why is FTP 95% of a 20-minute test?
Functional threshold power represents roughly the highest power a rider could sustain for about an hour. A maximal 20-minute effort sits above that, because a shorter effort draws on anaerobic capacity that cannot be held for sixty minutes. The 95% multiplier is the conventional discount applied to bridge the two. It is a population-level approximation: riders with large anaerobic capacity tend to be overestimated by it, and diesel-type riders underestimated.
What is a good watts per kilogram figure?
Power-to-weight is a ratio, not a grade, and what it means depends entirely on the duration it is measured over — a 5-second sprint figure and a 20-minute threshold figure are different quantities. Published comparison tables exist for each duration, but they describe distributions within tested populations rather than a target. The calculator returns the ratio and the durations it applies to; interpreting it against a table is a separate step.
Does TSS from different sports add up?
Only loosely. TSS is defined against cycling power with an hour at threshold scoring 100, and equivalents for running and swimming are built on different intensity measures. Summing them gives a rough workload picture rather than a physiologically equivalent total. Within cycling alone, where every session is scored against the same FTP, the numbers are directly comparable — provided that FTP is current.