- How do I convert pace to speed?
- Pace and speed are reciprocals. Speed (km/h) = 60 ÷ pace (min/km). So 5:00 min/km = 12 km/h. Going the other way, pace (min/km) = 60 ÷ speed (km/h). The PACE ↔ SPEED converter on this page does the math for both units (km/h and mph) live as you type.
- How do I convert min/km to min/mile?
- A mile is 1.609344 km, so min/mile = min/km × 1.609344. 5:00 /km = 8:03 /mi. 4:00 /km = 6:26 /mi. 6:00 /km = 9:39 /mi. Toggle KM ↔ MI at the top of the calculator to see your pace in both units instantly.
- What's a negative split and why does it matter?
- A negative split means running the second half of a race faster than the first half. Research consistently shows it produces faster overall times than positive or even splits, because you stay aerobic longer and have energy when others fade. Most world records — including the marathon — were set with negative splits. Pick "NEG" in the Splits section to plan one.
- What does PIN do?
- PIN tells the calculator which field is the output. The other two are inputs. The pinned field updates live as you edit the others. By default PACE is pinned — so you set distance and time, and pace is computed. Pin DISTANCE to plan "how far can I run in 45:00 at 5:00/km?". Pin TIME to plan "what time do I run 10K in at 4:30/km?".
- Can I share my calculation with someone?
- Yes. Every change updates the URL with your full state — distance, time, pace, units, split mode, predictor seed, everything. Copy the URL or hit SHARE to grab a clipboard-ready link. Sending it to a friend opens the calculator with exactly the same numbers you saw.
- How accurate is the race time predictor?
- It uses the Riegel formula T₂ = T₁ × (D₂ / D₁)^k with the Vickers-Vertosick (2016) distance-dependent exponent — k=1.06 short, climbing through 1.08 (half), 1.10 (marathon), 1.12 (ultras). That fixes Pete Riegel's original fixed-k=1.06 which underestimates marathon fade. Accurate to within ~2% for trained runners on flat courses; less accurate for first-time marathoners or hilly courses (in which case nudge k toward 1.10–1.15 manually). The connected coach goes further — see /coach.
- What's a good marathon pace?
- A "good" pace depends on training, age, and goals. As benchmarks: 4:00 marathon = 5:41 /km (9:09 /mi). 3:30 marathon = 4:58 /km (8:00 /mi). 3:00 marathon = 4:16 /km (6:52 /mi). Boston qualifying times for most age groups land between 3:00 and 4:00.
- Is my data saved or tracked?
- No accounts, no analytics that profile you, no server-side storage. Your unit preference and theme save to your browser's localStorage (purely client-side). Your calculator state lives in the URL so you can share it. Nothing else is captured.