How to Use This Calculator
Three modes:
- Pace from time + distance. "I want to run a 1:45 half marathon. What pace do I need?" Pick "Pace" mode, enter 1:45:00 and select Half Marathon.
- Time from pace + distance. "If I hold 8:00/mile, how long will my marathon take?" Pick "Time" mode, enter 8:00 pace and select Marathon.
- Distance from time + pace. "I ran for 45 minutes at 9:00/mile. How far did I go?" Pick "Distance" mode, enter time and pace.
Even Splits Beat Positive Splits Every Time
The split table is the most useful part of pace planning. The pattern that wins races: even splits or slightly negative splits (second half faster than the first). The pattern that wrecks races: positive splits — going out too fast and slowing down.
Print or screenshot the splits and use them on race day. At each marker, glance at your watch. If your time is ahead of the target, slow down. Almost every PR comes from runners who paced conservatively early.
Mile vs Kilometer
Quick conversion math: 1 mile = 1.609 km. So 8:00/mile = 4:58/km. 5:00/km = 8:03/mile. The calculator handles both — toggle units in the form.
Pace and Effort Aren't the Same
This calculator gives you mathematical pace. Real-world pace varies with hills, heat, wind, and fatigue. Heat in particular slows down pace meaningfully — every degree above 60°F costs you a few seconds per mile. Use the calculator to plan; adjust on race day for conditions.
For training paces (easy, marathon, threshold, interval, repetition), use the VDOT calculator instead. That gives you the right pace for each workout type, not just race pace.