Cycling Speed Calculator
Speed, time and distance for cyclists — plus the cube law that governs all of it: going 10 per cent faster costs 33 per cent more power, which is why your speed plateaus.
Cycling Speed Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Models no gradient, wind, surface, altitude or rider position.
- The cube law describes aerodynamic power only, not total power.
- Elapsed-time and moving-time averages differ substantially on stop-heavy routes.
- The distance projection table applies no fatigue model.
In short: Riding 40 km in 1:20:00 is 30.00 km/h, or 18.64 mph. The critical fact for any cyclist is that aerodynamic power scales with the cube of speed: raising 30 km/h to 33 km/h — just 10 per cent — requires roughly 33 per cent more power. Above about 25 km/h, air resistance, not fitness, is what limits you.
Formula
speed = distance ÷ time
Fdrag ∝ v² ⇒ Paero = F × v ∝ v³
P2 ÷ P1 = (v2 ÷ v1)³
Drag force rises with the square of velocity; power is force times velocity, so aerodynamic power rises with the cube. The ratio shown is the aerodynamic component only — total power also includes rolling resistance, which scales linearly, and gravity on a gradient.
Worked Example
- Convert distance to kilometres and time to hours.
- Divide for average speed in km/h; divide by 1.609344 for mph.
- Cube the speed ratio to obtain the aerodynamic power ratio.
- Compute the time saving from one additional km/h over the same distance.
- Apply the speed to standard distances for the projection table.
40 km in 1:20:00 → 30.00 km/h (18.64 mph, 8.33 m/s). Raising that to 33 km/h requires 1.1³ = 1.331, i.e. 33.1 per cent more aerodynamic power for a 10 per cent speed gain.
Strengths & Limits Of This Model
Where this engine is strong
- Explains the speed plateau with the physics that causes it
- Quantifies drafting against the cost of riding faster
- Every common unit printed at once
Where it stops
- Does not compute absolute power in watts — that needs rider and equipment data
- Average speed is a weak fitness metric across different routes
Practical Use Cases
Converting a ride into speed
Turns distance and elapsed time into km/h, mph and m/s at once.
Understanding a speed plateau
Shows why more training produces steadily smaller speed gains.
Valuing a drafting wheel
Puts the 25–30 per cent power saving alongside the cost of one extra km/h.
Planning a long ride
Projects finishing times for 20, 40, 100 and 160 km at your average.
Deciding where to spend money
Position and frontal area dominate at speed; weight matters mainly when climbing.
Methodology & Editorial Standards
The engine implements the standard published formula for this calculation. Inputs are validated for domain and sign before evaluation, and any undefined case returns an em-dash rather than a spurious value. Average speed is a pure ratio. The cube-law figures describe the AERODYNAMIC component of power only and are labelled as such in the engine output, because total power also includes rolling resistance and drivetrain losses that scale differently. No claim is made about absolute wattage, which depends on rider position, equipment and air density.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Cycling Speed Calculator — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What is a good average cycling speed?
For a recreational rider on flat roads, 20 to 25 km/h is typical; a fit club rider holds 28 to 32 km/h solo. But average speed is heavily dependent on terrain, wind, traffic and whether you rode in a group, so comparing your figure to someone else's tells you very little.
Why does going faster get so much harder?
Because aerodynamic power scales with the cube of speed. Going 10 per cent faster requires about 33 per cent more power, and 20 per cent faster requires about 73 per cent more. Above roughly 25 km/h nearly all your effort goes into moving air, so the returns diminish sharply.
How much power does drafting save?
Typically 25 to 30 per cent at moderate racing speeds, and more in a large, well-organised group. It is by far the largest single lever available to a cyclist — no training block delivers a 25 per cent power improvement, but sitting in a wheel does so immediately.
Should I buy a lighter bike or improve my position?
On flat or rolling terrain, position, almost always. At speed, 70 to 80 per cent of your power goes into pushing air and most of the frontal area is your body, not the bike. Weight matters primarily when climbing, where you are working against gravity rather than air.
Why is my average speed lower than my perceived effort?
Usually stops, junctions and freewheeling. Elapsed-time average includes every moment you were not moving; moving-time average excludes them. A ride with many junctions can show a two to three km/h difference between the two figures.
Does wind affect speed more than hills?
Over a loop course, often yes. Hills return some of the energy on the descent, whereas a headwind out and a tailwind back does not compensate evenly — you spend far longer riding into the wind than with it, so the slow section dominates the average.
What speed do I need to average for a century ride?
The engine prints the time for 160 km at your current average. A useful planning rule is that your sustainable average over a long ride is typically two to four km/h below your comfortable one-hour pace, because fatigue, stops and fuelling all accumulate.
Is the cube law exact?
The aerodynamic component follows it closely, but total power also includes rolling resistance, which scales roughly linearly with speed, and drivetrain losses. At low speeds where rolling resistance dominates, the cube relationship understates how easily speed comes; at racing speeds it is a very good approximation.
How much time does one extra km/h save?
Over 40 km at 30 km/h, about 155 seconds — over two and a half minutes. Whether that is worth the roughly 10 per cent extra aerodynamic power depends entirely on whether you can hold it for the whole distance.
Why do cyclists talk about watts instead of speed?
Because power is the input you control and speed is the output that conditions modify. The same 250 watts produces very different speeds into a headwind, up a hill, or in a group. Power is comparable across rides in a way that speed simply is not.
Does a heavier rider go faster downhill?
Generally yes, because gravitational force scales with mass while air resistance scales with frontal area, which does not increase proportionally. The same physics penalises heavier riders on the climb, and on most courses the climb costs more time than the descent returns.
What about e-bikes?
The arithmetic is identical — speed is still distance over time. The cube law applies equally, which is why most e-bikes are limited to around 25 km/h: beyond that the power demand rises steeply and battery range collapses.
How accurate is my bike computer's speed?
A wheel-magnet sensor is very accurate if the wheel circumference is set correctly, and noticeably wrong if it is not. GPS-only speed is less precise instantaneously but averages well over a ride. Discrepancies of one to two per cent between devices are normal.
Should I use average speed to measure fitness?
It is a poor measure across different rides, because route, wind and group riding swamp the fitness signal. Comparing the same route in similar conditions is more informative, and power output is better still.
What speed is 20 mph in km/h?
32.19 km/h. Multiply mph by 1.609344 for km/h, or divide km/h by the same figure for mph. The engine prints both simultaneously so the conversion never has to be done by hand.
Why does the projection table say it is arithmetic?
Because holding an average over 160 km is a fundamentally different task from holding it over 20, and no fatigue model is applied. The table multiplies your current average across distances; it does not predict what you could actually sustain.
Is this cycling speed calculator free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.