All tools

Free, fast, no signup. Pick a calculator, get your number, go run.

Summer essential

Heat & Humidity Pace Calculator

How much should you slow down today? Enter temperature and humidity, get your adjusted pace — with the science behind it.

 Race day

Marathon Fueling Calculator

How many gels, and when? Get a printable minute-by-minute fueling schedule for your marathon or half.

 Training

Pace Percentage Calculator

Workout says "95% of 5K pace"? Get the exact split — or flip it to find the race pace a workout implies.

Coming soon

Coming soon

Race-Time Predictor

Predict your marathon, half, or 10K time from a recent race result.

Coming soon

Treadmill Pace Converter

Match treadmill speed and incline to your real outdoor pace.

Coming soon

Printable Pace Bands

Generate a wrist-sized split band for your goal time, ready to print.

New tools ship regularly — bookmark this page to catch them first.