5K, 10K, Half & Marathon Distances in Miles and Km

Every standard race distance in both miles and kilometres, plus finish-time benchmarks so you know what each distance actually asks of you.

The core distances

5K = 3.107 mi · 10K = 6.214 mi · 15K = 9.321 mi · 10 miles = 16.09 km · half marathon = 21.0975 km = 13.109 mi · marathon = 42.195 km = 26.219 mi · 50K ultra = 31.07 mi.

Why a marathon is 26.2 miles

The 1908 London Olympic course was extended to 26 miles 385 yards so it could finish in front of the royal box. That distance was standardised in 1921 and never changed.

Track distances

One lap of a standard outdoor track = 400 m = 0.249 mi. A mile is 4 laps plus 9.34 m. 1500 m — the 'metric mile' — is 3.75 laps.

Typical finish times

5K: beginner 35–40 min, intermediate 25 min, competitive under 20. Marathon: first-timer 4:30–5:30, intermediate 3:45, competitive under 3:00.

Pace conversions

6:00/km = 9:39/mi · 5:30/km = 8:51/mi · 5:00/km = 8:03/mi · 4:30/km = 7:14/mi · 4:00/km = 6:26/mi. Multiply min/km by 1.60934 to get min/mi.

Predicting a longer race

Riegel's formula: T2 = T1 × (D2 ÷ D1)^1.06. A 25-minute 5K predicts roughly a 52-minute 10K and a 3:52 marathon if training supports the distance.

How this guide is researched and fact-checked

This article is produced by the ToolKit Pro Measurement Desk using ai-assisted research with human editorial verification against primary sources, and is checked by a human editor at the ToolKit Pro editorial desk before publication. Every number, formula and threshold quoted here is traced back to a primary standards body or health authority rather than to another blog, and each figure is re-computed with our own calculators so the worked examples and the live tools on this site always agree. When a definition changes — as with the 2019 SI redefinitions — the affected articles are re-checked and the “updated” date above is bumped.

Produced by: ToolKit Pro Measurement Desk — Unit conversion & measurement standards
Method: AI-assisted research, human-verified against primary sources
Reviewed by: ToolKit Pro editorial desk (human review)
Last reviewed: 2026-08-19
Corrections: spotted an error? Tell us and we will fix and re-date the page.

Sources & further reading

BIPM — The International System of Units (SI Brochure)
NIST — Guide for the Use of the International System of Units
WHO — Body weight & health guidance

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