Cycling speed from power calculator
At 200 W with 80 kg of rider and bike on flat ground, you hold roughly 33 to 34 km/h. Change power, weight, grade, wind or aerodynamics to see the steady speed and how much power goes to rolling, climbing and air drag. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Power
- 200
- Weight
- 80
- Grade
- 0
- Grade percent
- 0
- Grade fraction
- 0
- Cda
- 0.32
- Crr
- 0.005
This cycling speed from power calculator estimates the steady-state road speed you can hold for a given rider power in watts, total system mass, road grade, and aerodynamic drag parameters. It balances wheel power against rolling resistance, gravity on a grade, and cubic air drag so training zones, event pacing, and what-if equipment changes stay grounded in physics rather than guesswork. Defaults match common road assumptions: CdA about 0.32 square metres, rolling resistance 0.005, sea-level air density 1.225 kilograms per cubic metre, and a 97.5 percent drivetrain efficiency. A typical check is two hundred watts with eighty kilograms total mass on flat ground, which yields roughly thirty-three to thirty-four kilometres per hour depending on rounding. The engine is fully deterministic: no network calls, no sampling, and no date-dependent shortcuts.
How steady speed is worked out from power
At constant speed on a smooth road the mechanical power delivered to the wheel equals the power consumed by the three classical resistive channels: rolling resistance of the tires on the pavement, the gravitational component along the slope, and aerodynamic drag from the rider and bike cutting through the air. Rolling and gravity forces are essentially independent of speed for a fixed grade, so their power grows linearly with velocity.
Aero force grows with the square of relative airspeed, so aero power grows roughly with the cube of ground speed when wind is calm. This calculator multiplies rider power by drivetrain efficiency to obtain wheel power, builds the resistive force from total mass, gravity, coefficient of rolling resistance, and the grade angle, then solves for the unique non-negative ground speed that closes the power balance. Non-positive total weight is always rejected because mass must be positive for the force model.
Use dedicated tools for interval structure, heart-rate zones, or route elevation profiles; this page answers only the power-to-speed mapping under a steady ride assumption.
Where power-to-speed estimates fit in training, events, and software
Athletes use steady speed from power when converting a threshold watt target into an expected road speed for flat time trials, when checking whether a climb grade and power plan are realistic before race day, or when comparing aero positions by changing CdA while holding power and mass fixed. Coaches generate pacing tables for groups of riders with different total weights on the same course profile without inventing speeds by feel.
Equipment discussions become quantitative: a small CdA drop at two hundred fifty watts can matter more on the flat than a few watts of tire Crr, while on a five percent climb the gravity term dominates and mass savings show up immediately. Product and education tools use the split of rolling, gravity, and aero power when teaching why high speeds are so expensive in watts.
Pair it with pace or heart-rate helpers when you need related training metrics, and keep grade and wind honest so the estimate matches the road you will actually ride.
What you can do with it
Threshold and time-trial pacing
Convert a target power and total mass into expected flat or mild-grade speed for time-trial and race plans.
Climb and descent what-ifs
Vary grade, mass, and watts to see how climb speed and downhill free-speed shift before an event.
Aero and equipment comparisons
Hold power fixed and change CdA or Crr to quantify speed gains from position, kit, or tire choices.
FAQ
What does the cycling speed from power calculator cost?
It is free in your browser on this page.
Why must weight be positive?
Total system mass (rider plus bike and kit) enters the rolling and gravity forces.
Is grade entered as percent or as a fraction?
Percent by default: 5 means a 5% climb. Negative values are descents.
What do CdA and Crr mean?
CdA is aerodynamic drag area in m² (drag coefficient times frontal area). Crr is the dimensionless rolling-resistance coefficient of the tires on the road.
Does this model include acceleration, drafting, or stop signs?
No. It estimates steady-state speed only for constant power and constant grade with optional along-path wind. It is not a full route simulator.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/health/cycling-speed-power \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"power":200,"weight":80}'const res = await fetch("https://api.kit.forhosting.com/health/cycling-speed-power", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"power": 200,
"weight": 80
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/health/cycling-speed-power",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"power": 200,
"weight": 80
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/health/cycling-speed-power", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"power":200,"weight":80}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"power":200,"weight":80}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/health/cycling-speed-power", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"power": 200,
"weight": 80
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "health.cycling_speed_power",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_power_w | 5000 |
max_weight_kg | 500 |
max_grade_pct | 50 |
max_cda | 2 |
max_abs_wind_ms | 40 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Use it free in the browser for workouts and race prep, or call the API at $0.002 per successful request when you need reproducible speed estimates in training software, spreadsheets, or automated plans.
What steady-state power balance means and what the response contains
The response returns speed in metres per second, kilometres per hour, and miles per hour; echoes power, weight, grade as percent and fraction; reports CdA, Crr, air density, efficiency, wind, and g; and splits forces and power among rolling, gravity, and aero so you can see which term dominates. The method tag is steady_state_power_balance. There is no weather API, no GPS track, and no stochastic sampling: the engine either finds a finite steady speed inside the supported limits or rejects the input with invalid_input.
How power, weight, grade, and drag fields are read
Optional CdA defaults to 0.32 square metres, Crr to 0.005, air density rho to 1.225 kilograms per cubic metre, efficiency to 0.975, wind to zero metres per second with positive as headwind, and g to 9.80665. Scientific notation and optional leading plus signs are accepted when they parse as finite decimals; blank strings, hex prefixes, and non-numeric tokens fail with a clear message. Power must be non-negative and within the power ceiling. CdA, rho, and efficiency must stay positive within their ranges. The preferred fields are power for watts at the pedals and weight for total system mass in kilograms, with aliases such as watts and power_w for power and mass, kg, total_mass, and m for weight. Grade defaults to zero flat and is interpreted as percent unless grade_unit is set to fraction or ratio; five means a five percent climb, and negative values model descents. An optional precision field controls decimal places on numeric outputs, defaulting to four and capped at fifteen so JSON goldens stay stable. Weight must be strictly positive and within the documented mass ceiling; zero or negative mass fails with invalid_input naming weight. Pair the free browser run on this page with the priced API when you need identical numbers inside automated training pipelines without re-implementing the cubic aero model yourself.
Where power-to-speed estimates fit in training, events, and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a desk check to an automated pipeline without changing the mathematical result.