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Common Length Conversions

The conversion factors worth memorising, and mental-math shortcuts for the rest.

1 inch = 2.54 cm. 1 foot = 30.48 cm. 1 mile ≈ 1.61 km. Almost everything else derives from these.

Length conversions come up constantly — recipes, furniture, travel, fitness. Four or five factors cover almost every real case.

Part of: Unit Conversion Tools

Quick answer

1 inch = 2.54 cm. 1 foot = 30.48 cm. 1 mile ≈ 1.61 km. Almost everything else derives from these.

What you are trying to do
The conversion factors worth memorising, and mental-math shortcuts for the rest.
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Length Converter
Limit to remember
Treat this as a practical aid for the task, not a replacement for professional judgment.

Key points

  • ▸ 1 inch = 2.54 cm (exactly, by international agreement in 1959).
  • ▸ 1 foot = 12 inches = 30.48 cm ≈ 0.3 metres.
  • ▸ 1 yard = 3 feet = 0.9144 metres.
  • ▸ 1 mile = 1.609 km. Mental math: miles × 1.6, or miles + (miles × 0.6).
  • ▸ 1 metre ≈ 3.28 feet ≈ 39 inches. 1 km ≈ 0.62 miles.

Examples

  • Height: 5'10" to metres
    5 × 30.48 + 10 × 2.54 = 152.4 + 25.4 = 177.8 cm = 1.778 m.
  • Marathon: 26.2 miles to km
    26.2 × 1.609 = 42.16 km. Mental approx: 26 + 26 × 0.6 = 26 + 16 = 42.
  • Bedroom: 12 ft × 10 ft to metres
    12 × 0.3048 = 3.66 m, 10 × 0.3048 = 3.05 m. So 3.66 m × 3.05 m.

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Frequently asked questions

› Is inch exactly 2.54 cm or is it approximate? Trust & accuracy

Exactly. Since 1959, the international inch is defined as exactly 2.54 cm. Before that it was a fraction off, which is why old conversions sometimes disagree at the fifth decimal.

› Why do UK miles and US miles equal? Troubleshooting

Both use the international mile (1609.344 m exactly). The UK also uses the statute mile for some surveying — same value. US survey miles are slightly different but rarely encountered.

› How accurate are online calculators and converters? Trust & accuracy

Online calculators are only as accurate as the numbers, units, assumptions, and rounding choices you enter. Recheck the input values first, then compare the formula against your real situation. For legal, tax, medical, financial, or professional decisions, treat the result as a planning estimate, not advice.

› What inputs should I double-check first? Troubleshooting

Double-check units, dates, percentages, decimal placement, and whether the input is before-tax, after-tax, gross, net, original, or final. Most calculator mistakes come from feeding the right formula the wrong base. If the result feels off, rebuild it from a simple worked example.

› Why do two calculators sometimes give different answers? Comparison

Two calculators may round at different steps, use different defaults, or interpret the same label differently. Percent, time, finance, and unit tools are especially sensitive to basis and rounding rules. Compare the formula, not just the final number, before deciding which result to trust.