Length Conversion
Metric and imperial distance units
Required Parameters
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Quick Answer
1 inch = 25.4 mm exactly. 1 foot = 0.3048 m. 1 mile = 1.609 km. Each conversion between metric and imperial length uses exact definitions established by international agreement in 1959.
Length Conversion Calculator
Convert between length units: meters, centimeters, millimeters, inches, feet, mils, and micrometers.
Key Conversions
- 1 inch = 25.4 mm = 2.54 cm
- 1 mil = 0.001 inch = 0.0254 mm
- 1 foot = 12 inches = 304.8 mm
Design Notes
PCB design commonly uses mils (thousandths of an inch) for trace width and via diameter, while board dimensions may be in mm. The exact definition (1 inch = 25.4 mm) ensures zero conversion error between systems.
Common Mistakes
- 1
Confusing mils (thousandths of an inch) with millimeters — 1 mil = 0.0254 mm, not 1 mm.
- 2
Forgetting that yards and meters are close but NOT equal: 1 yard = 0.9144 m (about 9% shorter).
- 3
Using different precision than the measurement justifies — a ruler measurement to 1 mm does not justify 6 decimal places after conversion.
Knowledge Base
How many mm in an inch?
Exactly 25.4 mm. This is the international standard (since 1959). 1 inch = 25.4 mm = 2.54 cm. This exact definition means metric-imperial conversions for length are precise, not approximate.
How do I convert inches to centimeters?
Multiply inches by 2.54. Example: 12 inches = 12 × 2.54 = 30.48 cm. For quick mental math: 1 inch ≈ 2.5 cm (1.6% error). Reverse: divide cm by 2.54 to get inches.
How many feet in a meter?
1 meter = 3.28084 feet. 1 foot = 0.3048 meters exactly. For quick conversion: 1 meter ≈ 3 feet 3.4 inches. Common pairs: 6 feet = 1.83m, 5 feet = 1.52m.
What is a mil (thou)?
1 mil = 1 thousandth of an inch = 0.001 inch = 0.0254 mm = 25.4 µm. Used for PCB trace widths, wire insulation thickness, paint coating thickness, and precision machining tolerances. Not to be confused with millimeters.
How do I convert between metric prefixes?
Move the decimal point: 1 km = 1000 m, 1 m = 100 cm = 1000 mm, 1 mm = 1000 µm, 1 µm = 1000 nm. Each prefix step is ×1000 or ×10: kilo (10³), centi (10⁻²), milli (10⁻³), micro (10⁻⁶), nano (10⁻⁹).
What is the difference between nautical miles and statute miles?
1 nautical mile = 1.852 km = 1.151 statute miles. Nautical miles are based on Earth's geometry: 1 nautical mile = 1 minute of arc of latitude. Used in aviation and maritime navigation because they simplify navigation calculations on charts.
What are common PCB dimension units?
PCB dimensions use a mix: board size in mm or inches, trace width in mils (thousandths of inch) or mm, via diameter in mils, component pitch in mm (0.5mm, 0.8mm, 1.27mm, 2.54mm). 1 mil = 0.0254 mm. Standard via: 10 mil drill, 20 mil pad.
How do I convert between yards and meters?
1 yard = 0.9144 meters exactly. 1 meter = 1.0936 yards. For quick estimation, yards and meters are nearly equal (within 10%). 100 yards = 91.44 meters. A football field (100 yards) is about 91.4 meters.
What is the difference between US and Imperial fluid measurements?
Length units are the same in US and Imperial systems (inch, foot, yard, mile). The differences are solely in volume units: 1 US gallon = 3.785 L vs 1 Imperial gallon = 4.546 L. Length conversions are universal across both systems.
What precision should I use for length conversions?
Match the precision of your input. If measuring with a ruler to 1mm, converting to inches gives 3 significant figures max. For machining: use 4-6 decimal places. For construction: nearest 1/16 inch or 1mm. For PCB design: 0.1 mil or 0.01mm resolution.