Every run gets you closer
to your next PB.

Free, fast tools that answer the questions runners actually Google — pacing, heat, fueling — so you train smarter and race faster. No account, no tracking, no 2,000-word intro before the tool.

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.

Why Run4PB?

Most running calculators are buried under ads or padded with SEO filler. Run4PB does the opposite: the tool loads first, works on your phone at 6 a.m. before a run, and explains its method in plain language below the results — so you can trust the number, not just copy it.

More tools are on the way: race-time predictor, treadmill conversion, printable pace bands. See all tools.