About
Last updated: 2026-06-25
RunCalc is a free suite of running calculators for running pace, marathon race time prediction, calories burned, and treadmill conversion.
Every calculation runs in your browser, and we provide it transparently based on widely used standard formulas.
What is RunCalc
RunCalc is a free set of tools that help anyone who enjoys running compute pace, times, calories, and speed quickly and accurately. It handles seemingly complex pace conversions and race predictions from simple inputs, and openly shows the formulas it uses.
Operating principles (E-E-A-T)
- Experience — results are built around the distances runners actually use (5K, 10K, half, full marathon) and goals like sub-3 and sub-4.
- Expertise — we use well-validated formulas: pace = time ÷ distance, the Riegel race prediction, MET-based calorie estimates, and speed-pace conversion.
- Authoritativeness — we follow standard references such as the official marathon distance (42.195 km) and MET values from the Compendium of Physical Activities.
- Trustworthiness — we never hide the formulas, and we clearly mark estimate-based items (race prediction, calories, incline adjustment) as for reference. Inputs are never collected or stored.
Formulas and standards used
The formulas and constants used in each calculator are listed below. Some constants (the Riegel exponent, incline adjustment rate, etc.) vary by individual and can be adjusted in the code's tunable constants.
- Pace — pace (min/km) = total time ÷ distance, speed (km/h) = 60 ÷ pace
- Race prediction — Riegel formula T2 = T1 × (D2 ÷ D1)1.06
- Calories — calories (kcal) = MET × body weight (kg) × time (hours), with MET applied by speed
- Treadmill — pace ↔ speed = 60 ÷ value, assuming about a 3% intensity increase per 1% incline
A note on accuracy
All RunCalc results are estimates for reference based on your inputs and the published formulas. In particular, marathon race prediction assumes adequate long-run training and grows less accurate as the distance gap widens, and calories burned and incline adjustment vary with terrain, temperature, and individual efficiency. Please prioritize actual race results or measured device values.
Contact
Send suggestions or error reports to jin@zerolabskorea.com. For how we handle personal data, see our Privacy Policy.
Last updated: 2026-06-25