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What is a inch?

The global standard for screen sizes, pipe diameters and Anglo-Saxon shoe sizes

Definition

The inch equals 2.54 centimeters exactly since 1959. It is the global standard for screen diagonal sizes — a "55-inch TV" has a 139.7 cm diagonal. Pipe diameters, US and UK shoe sizes, and hard-drive form factors are all specified in inches. 1 inch = 1/12 foot = 1/36 yard.

Common uses

  • Screen and monitor diagonals worldwide (phone, tablet, TV)
  • US and UK shoe sizes
  • Industrial pipe and fitting diameters

🌍 Real-world scale

A 65-inch TV has a 165 cm diagonal. A smartphone screen is typically 6–7 inches. Standard copper plumbing in the UK is ½ inch or ¾ inch.

Convert from inches

14 conversions
Inch to Meter1 in = 0.0254 mInch to Kilometer1 in = 2.5400e-5 kmInch to Centimeter1 in = 2.54 cmInch to Millimeter1 in = 25.4 mmInch to Mile1 in = 1.5783e-5 miInch to Yard1 in = 0.02778 ydInch to Foot1 in = 0.08333 ftInch to Nautical Mile1 in = 1.3715e-5 nmiInch to Micrometer1 in = 25,400 µmInch to Nanometer1 in = 25,400,000 nmInch to Light Year1 in = 2.6848e-18 lyInch to Furlong1 in = 0.0001263 furInch to Fathom1 in = 0.01389 ftmInch to Angstrom1 in = 254,000,000 Å

Convert to inches

14 conversions
Meter to Inch1 m = 39.3701 inKilometer to Inch1 km = 39,370.08 inCentimeter to Inch1 cm = 0.3937 inMillimeter to Inch1 mm = 0.03937 inMile to Inch1 mi = 63,360 inYard to Inch1 yd = 36 inFoot to Inch1 ft = 12 inNautical Mile to Inch1 nmi = 72,913.39 inMicrometer to Inch1 µm = 3.9370e-5 inNanometer to Inch1 nm = 3.9370e-8 inLight Year to Inch1 ly = 3.7247e17 inFurlong to Inch1 fur = 7,920 inFathom to Inch1 ftm = 72 inAngstrom to Inch1 Å = 3.9370e-9 in

Tips

  • 1 inch = 2.54 cm exactly by international agreement — no rounding.
  • Screen sizes are always diagonal, never width. A 27-inch monitor is about 60 cm wide.
  • To convert cm to inches mentally, divide by 2.5 and subtract 1.6%.

Common mistakes

  • Reading a screen size as width. A 65-inch TV is about 143 cm wide — the 165 cm figure is diagonal.
  • Using 2.5 instead of 2.54 on precision drawings — the 1.6% error matters in manufacturing.
  • Confusing inches of length with inches of mercury (inHg) — a pressure unit, not length.

FAQ about the inch

What is a inch?
The inch equals 2.54 centimeters exactly since 1959. It is the global standard for screen diagonal sizes — a "55-inch TV" has a 139.7 cm diagonal. Pipe diameters, US and UK shoe sizes, and hard-drive form factors are all specified in inches. 1 inch = 1/12 foot = 1/36 yard.
Where is the inch used?
The inch is commonly used for: Screen and monitor diagonals worldwide (phone, tablet, TV); US and UK shoe sizes; Industrial pipe and fitting diameters.
What is an example of a inch in real life?
A 65-inch TV has a 165 cm diagonal. A smartphone screen is typically 6–7 inches. Standard copper plumbing in the UK is ½ inch or ¾ inch.
What category does the inch belong to?
The inch is a unit of length, part of the 15-unit length category on UnitConv.
How accurate are inch conversions?
All conversion factors follow NIST and BIPM international standards to 8 significant figures — the highest practical accuracy.
Explore all 15 length units and their conversions.📏 Length hub →