SnapMyGym
Convert distance and time into pace and speed, with finish-time projections for 5K through marathon. Free, no signup.
Enter a distance and time to get your pace per mile and kilometer, your speed, and projected finish times from 5K to the marathon. Projections use Riegel's formula — the standard for translating one race effort into realistic targets at other distances.
Riegel's formula (T2 = T1 × (D2 ÷ D1)^1.06) models how pace decays as distance grows. It's remarkably accurate from 5K to half marathon for trained runners; marathon projections assume the long-run mileage is in the bank — without it, real marathons come in slower than the math.
Even pacing wins races. Most personal bests are run with the second half as fast as or faster than the first, and going out 10 seconds per mile too fast typically costs 30 or more seconds per mile over the final quarter.
Around 30 minutes is a solid recreational benchmark, 25 minutes is decidedly fit, and under 20 minutes puts you near the front at most local races. If you're a lifter carrying muscle, judge yourself on your own trend rather than pure-runner benchmarks.
Run a recent shorter race or an honest time trial, then project with Riegel's formula rather than guessing from training runs. Aim for even splits: reach halfway feeling controlled, then squeeze the second half.
Within about 1–2% between 5K and half marathon for runners with appropriate training. It's least reliable for the marathon, where fueling and long-run preparation matter as much as raw speed.
Want the number to actually go up? Snap My Gym builds percentage-based programs around your lifts and tracks them automatically. More evidence-first training articles on the blog.