Sports calculators for swimming, cycling and running
Eight free calculators for endurance athletes: the watts you push on a climb, your swim CSS pace, your power profile, your running paces from a single test, grade adjusted pace and a race time prediction for an Olympic distance triathlon, a 70.3 or a 140.6. No sign-up, nothing to install, and your data never leaves your browser.
You can also explore your frontal area and CdA using photos and compare posture and equipment scenarios in the aerodynamics lab.
Which calculator you need, depending on what you want to know
Almost every question an endurance athlete asks fits into four: what pace should I train at, how much effort am I really producing, what time can I run on race day and how much will the terrain cost me. Each calculator on this site answers one of them.
| If you are asking… | Use | You need |
|---|
| What pace for my swim sets? | Pace and CSS | A 400 m and a 200 m test |
| How many watts am I pushing on this climb? | Climbing watts | Weight, gradient and average speed |
| Am I more of a rouleur or a climber? | Power profile | Your best 5 s, 1, 5 and 20 min watts |
| What pace should each zone be? | Paces from a test | A 1 km, 5 km or 12 minute test |
| What does this elevation cost me? | Grade adjusted pace | Your flat pace and the gradient |
| What time will I do in my 70.3? | Race time predictor | CSS, watts and run pace |
| How much slower will I run off the bike? | Run off the bike | Your best time at that distance |
If you are starting from nothing and have no data, this order works best: do a running test and a swim test first, because they are free and need only a stopwatch. That already gives you your training paces and your CSS. The cycling side can wait until you have a power meter, or be approximated with the climbing watts calculator, which estimates power from the physics of movement rather than measuring it.
Why these calculators show you the formula
A calculator that only spits out a number forces you to believe the number. Here every page includes the equation in plain text, the assumptions that were made and the expected error margin, because in endurance sport the margin matters as much as the result.
An example. The power on a climb splits between three terms, and as soon as the gradient passes 5 % one of them swallows the others:
P = (m · g · sin θ · v) + (m · g · Crr · cos θ · v) + (½ · ρ · CdA · v³)
gravity rolling aerodynamics
That is why estimating watts on an 8 % climb is reliable to within 3-5 % even if you do not know your CdA, and why the same estimate on the flat is worthless: on the flat the third term, which depends on the cube of speed and on a frontal area you have never measured, is almost everything. Knowing that changes how you read the result.
The same applies to critical speed in swimming, to the energy cost of gradient in running, and to the accumulated fatigue factor in a triathlon prediction. Every one of them has a published formula behind it, and every one has an error range worth knowing before you plan a race around it.
Where the models come from
None of these calculators invents its model. The cycling one uses the power equation of Martin and colleagues (1998); the swimming one, Wakayoshi's critical swim speed; the power profile builds on the critical power model of Monod and Scherrer and the Coggan and Allen power profile categories; the gradient adjustment uses the energy cost curve of Minetti and colleagues (2002). Each page cites the model it applies and explains what it simplifies in applying it.
Frequently asked questions
Are they free, and do I need an account?
They are free and there is no sign-up. No account, no trial, no paid tier. The site is funded by advertising and by the commission on the training logs linked at the end of each calculator.
Is the data I enter stored anywhere?
No. Every calculation runs in your browser in JavaScript: the numbers you type are never sent to a server and are never stored. Close the tab and they are gone.
Do they work on a phone?
Yes. They are built to be used one-handed at the poolside or after a ride, and they need no connection once the page has loaded.
Can I use them if I don't do triathlon?
Yes. The cycling ones serve any cyclist, the running ones any runner and the swimming one any distance swimmer. Only the two in the triathlon section assume you are chaining all three disciplines.
How often should I redo the tests?
Every six to eight weeks during a normal season, and always after a specific block of work. Repeating them fortnightly usually measures how fresh you are that day rather than your actual fitness.
What languages is the site in?
Spanish, English and French. Each calculator has its own translated version, with the same formulas and the same reference tables; you can switch language from the selector in the header.
The aerodynamics lab is experimental: it combines traced area with editable assumptions and a generic geometric torso; its output is not validated as a CdA measurement.
Disclaimer and privacy
This calculator is an informational estimate and does not replace a coach or a laboratory test. Nothing you type ever leaves your browser.
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