Runnerslab.app

Runners Lab is a free website of running calculators. You open a tool, type a few numbers, and get an answer. That is the whole product.

There is no signup. There is no training diary. The math runs in your browser, so the same inputs always give the same outputs.

The site lives at runnerslab.app.

What you can calculate

The tools fall into a few simple groups:

Pace. How fast you need to run for a 5K, 10K, half marathon, marathon, or any other distance. You can also convert pace to speed.

Races. Turn a goal time into kilometre or mile splits. Predict what a recent result might be worth at another distance. Build even, negative, or progressive split tables.

Training. Estimate easy, tempo, threshold, and interval paces from a recent race.

Heart rate. Get training zones from age, a known max heart rate, or heart-rate reserve.

Performance. See what a hilly run would have been worth on the flat, or how a race time compares with age-graded standards.

You pick a tool, get the number you need, and move on. If you want another question answered, you open another tool.

How the numbers work

Some answers are just arithmetic. Pace is finish time divided by distance. Splits divide a target time across kilometres or miles. If the inputs are right, you get the same number you would get with a stopwatch and a measured course.

Some answers are estimates. Those use well-known published formulas, such as Riegel for race prediction, Daniels VDOT for training paces, Tanaka for heart-rate zones, Minetti for hills, and WMA age-grading for “how good is my time?”

The site is honest about the difference. Exact tools do math. Model tools cite the formula they use. Nothing here is guessed by AI.

What it is not

Runners Lab is not a coach, a wearable, or a fitness app. It will not write you a plan, track your miles, or tell you that you are ready for a marathon.

It is a digital lab: search, calculate, get an answer, open another tool.

If you want the numbers, open a calculator. If you want the formulas, read the methodology.