Half Marathon Pace Calculator

How to use the half marathon pace calculator

What this calculator does

This calculator turns a race distance and finish time into an average running pace, an equivalent pace in the other common distance unit, average speed, and estimated checkpoint times. It is useful for setting a race target, preparing a pacing card, comparing a completed result with a goal, or converting between min/km, min/mile, km/h, and mph. A half marathon is officially 21.0975 km, or about 13.1094 miles, as described by World Athletics' half marathon overview. The result is an arithmetic average; it does not predict fitness, account for hills or weather, or guarantee that a target is physiologically appropriate.

When to use it

Use it before a race to translate a goal time into a pace you can recognize on a watch, during training to plan goal-pace repetitions, after a race to understand your average performance, or when a plan uses a different unit system from your usual one. It can also create an Excel workbook for a coach, training log, or personal race plan.

How to calculate

1. The calculator opens with a complete demonstration: Half marathon, 21.0975 km, and 1:45:00. The example results and a validated Excel workbook are available immediately.
2. Choose Event. Standard selections fill the official or conventional race distance; choose Custom distance to type another value.
3. Enter Distance with a decimal point and choose km or mi. Then enter Hours, Minutes, and Seconds for the target or recorded finish time.
4. Select the Primary pace unit and Primary speed unit. These controls change which equivalent is emphasized without changing the underlying performance.
5. Read the live pace, speed, finish-time, distance, and checkpoint results. Select Download Excel to export the current validated state. Reset clears the demonstration and all semantic data; Excel export then remains unavailable until a complete valid state is entered again.

Input guide

Event is required and accepts Half marathon, Marathon, 10K, 5K, or Custom distance. Selecting Half marathon supplies 21.0975 km. Changing the distance manually changes the event to Custom distance so the label never implies a standard course length that is no longer present.

Distance is a required positive decimal measured in the adjacent km or mi selection. For example, enter 21.0975 km or 13.1094 mi. A decimal point is accepted; a decimal comma, scientific notation, mixed units, zero, negatives, and values above the 1,000 km safety limit are rejected instead of being silently reinterpreted. Increasing distance while holding time constant produces a faster pace and higher speed.

Hours, Minutes, and Seconds are required whole-number time components. Hours may be 0-99; minutes and seconds must each be 0-59. The combined time must be greater than zero. For a 1 hour 45 minute finish, use 1, 45, and 0. A common mistake is entering 105 in Minutes; enter 1 hour and 45 minutes instead.

Primary pace unit accepts min/km or min/mile. Primary speed unit accepts km/h or mph. These required display controls do not alter the calculation; they choose the emphasized equivalent. NIST explains why length and time units combine into derived quantities such as velocity in its guide to SI units.

Output guide

The header pills summarize Pace, Speed, Finish, and Distance. Average pace is finish time divided by distance and is rounded to the nearest displayed second. Equivalent pace is the same performance converted to the alternate distance unit. Average speed and Alternate speed express distance per hour; higher speed corresponds to lower time-per-distance pace. Finish time and Race distance restate the validated inputs so the result remains auditable.

The Estimated checkpoint splits table lists checkpoint name, distance in kilometers, distance in miles, and elapsed time. Each row assumes exactly even pacing. A high split time means slower average progress; a low split time means faster progress. The final row must equal the entered finish time. These are planning estimates rather than recommended race tactics.

Worked example

With the startup values, total time is 1:45:00, or 6,300 seconds. Dividing 6,300 by 21.0975 km gives 298.6136 seconds per kilometer, which displays as 4:59 min/km. Converting the distance to miles gives about 13.1094 miles; 6,300 divided by that distance gives 480.5720 seconds per mile, displayed as 8:01 min/mile. Dividing 21.0975 km by 1.75 hours gives 12.06 km/h, equivalent to 7.49 mph. The final checkpoint is exactly 1:45:00.