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FitCalc

Seventeen training calculators in one tool, with the formulas shown side by side where they disagree. Built for my own training.

Year
2026
Track
built
Category
tool

Tools

  • Next.js
  • CSS Modules

Body, run, bike, strength. Energy needs from Mifflin-St Jeor or Katch-McArdle, gear ratios against wheel circumference, tire pressure off measured casing width, one-rep max through three estimators at once so you can see how far apart they sit.

Every screen shows its own working. The notes under each result say what the number cannot tell you, which is usually the more useful half.

Modernist Bauhaus, and entirely mine. I built it because I wanted it, and I send it to friends who train.

Screens

  1. The one-rep max screen, headed Three estimators side by side so you can see where they disagree. A large 115.5 kg sits beside a matrix of predicted load by formula, Epley against Brzycki against Lombardi down eleven rep counts, every cell shaded by value. The notes say two of them agree exactly at ten reps and diverge either side of it.
    The claim the whole tool rests on. Where three formulas disagree, it prints all three.
  2. Gear ratios. A shaded table gives the speed that every chainring and cog combination produces at ninety revolutions per minute, two rings across eleven cogs. The panel beside it reports a 428 percent range, 29 to 122 gear inches, and the wheel circumference the figures came from. The accent turns blue for the bike section.
    Every combination on the bike, as the speed it actually produces.
  3. Tire pressure. Two gauges read 3.17 and 4.37 bar for front and rear, worked from a system mass, a measured casing width and a chosen surface. The notes underneath name the model and the point it was calibrated at, then say the number is an estimate, never to exceed the sidewall maximum, and that comfort and grip usually beat it.
    The notes under a result say what it cannot tell you, which is usually the more useful half.
See it running

More work

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