How to Calculate Half Marathon

What is Half Marathon?

A half marathon is 21.0975 km (13.1094 miles). The pace calculator converts your target finish time into min/km or min/mile pace.

Formula

Time = Distance / Pace | Pace = Time / Distance | VO₂ impact ≈ 2.5 min per mile slower than 5K pace

Step-by-Step Guide

1Pace per km (sec) = Total seconds / 21.0975
2Convert to MM:SS for practical use
3Speed km/h = 21.0975 / (total seconds / 3600)
4Even splits ±5 sec/km is optimal race pacing

Worked Examples

Input

Target 1:55:00

Result

Pace = 5:28/km or 8:47/mile; Speed = 10.97 km/h

Frequently Asked Questions

What is Half Marathon Is 21?

A half marathon is 21. 0975 km (13

How accurate is the Half Marathon Is 21 calculator?

The calculator uses the standard published formula for half marathon is 21. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

What units does the Half Marathon Is 21 calculator use?

This calculator works with inches, kilometres, miles, kilometres per hour. You can enter values in the units shown — the calculator handles all conversions internally.

What formula does the Half Marathon Is 21 calculator use?

The core formula is: Pace per km (sec) = Total seconds / 21.0975. Each step in the calculation is shown so you can verify the result manually.

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