Length Converter

Convert length units instantly: mm, cm, m, km, inches, feet, yards, miles, and nautical miles. Type a value in any unit to see all conversions in one grid.

Construction Blueprints, Fabric Yards, and Survey Chains

BrainyCalculators editorial insight — unique to this tool

US construction drawings dimension in feet and inches (e.g., 8'-6") while metric projects use millimeters — a 2×4 stud is actually 1.5" × 3.5" nominal, not 2" × 4". Fabric and upholstery still sell by the yard in the US (1 yd = 91.44 cm) while EU retailers quote meters per roll. Land surveyors in Commonwealth countries may reference chains (1 ch = 20.1168 m) on older title deeds, and aviation uses nautical miles (1 NM = 1.852 km) for chart distances.

When to use this calculator

Convert linear distance when reading blueprints, sewing patterns, running tracks, or GPS legs — not area (sq ft) or volume (cubic yards).

Reference	Value	Context
1 inch	25.4 mm	Exact by international agreement
1 mile	1.609 km	Road vs statute
1 nautical mile	1.852 km	Charts and aviation
Regulation basketball hoop	10 ft	3.05 m rim height

Not what you need? For land area in acres or hectares, use Area Converter. For room floor dimensions to square footage, convert length here then multiply — or use Area Converter directly.

Converting weight, temperature, or multiple unit types?

This page converts length/distance only. For mass, temperature, and more in one tool, use the Unit Converter →

Value

From Unit

Enter a value above to see all unit conversions.

What is a Length Converter?

A length converter translates one-dimensional distance between metric and imperial units — millimetres to miles, feet-and-inches to metres, nautical miles to kilometres. Use it for blueprints, fabric yardage, running distances, and travel planning where the question is “how long?” not “how heavy?” or “how hot?”

This page is dimension-specific with reference anchors for construction (8′-6″ vs 2.59 m), fabric (yards vs metres), and survey work. It does not convert area (square feet) or volume (cubic yards) — squaring or cubing length units requires the Area or Volume Converter.

For mass (kg, lb, stone), use the Weight Converter. For temperature (°C, °F, K), the Temperature Converter. For length, weight, temperature, and more in one tool, use the Unit Converter.

Length Anchors for Build and Travel

1 inch (exact) = 25.4 mm

8′-6″ run = 2,590.8 mm

1 nautical mile = 1.852 km

1 statute mile = 1.609 km

100 m sprint = 328.1 ft

1 chain (survey) = 66 ft

1 light-year = 9.461×10¹² km

Credit card width = 85.6 mm

Worked Examples: CNC, Fabric, and Survey Chains

1

8′-6″ drawing to millimetres

Total inches = 8×12 + 6 = 102 in. × 25.4 = 2,590.8 mm for the CNC program.
2

3 yards of fabric to metres

3 yd × 0.9144 = 2.743 m. Compare per-metre price against a US per-yard quote after converting.
3

Nominal 2×4 actual size

1.5 in × 3.5 in → 38.1 mm × 88.9 mm. Do not feed nominal 2 in into a metric cut list.
4

10 km race vs 10 mi race

10 km = 6.21 mi. Length conversion only — course area or elevation gain needs other tools.

How the Length Converter Works

Formula, assumptions, and calculation steps for this conversion tool.

Methodology

Conversion calculators multiply by fixed conversion factors after identifying the source and destination units.

Calculation Steps

Choose the input unit and output unit.
Enter the amount to convert.
Apply the standard conversion factor.
Return the converted value with unit labels.

Assumptions and Limits

Conversions use standard factors unless a regional variant is selected.
Rounding is applied for readability.
Temperature and pressure conversions may require formulas rather than simple multiplication.

Frequently Asked Questions

How many millimetres is a 2x4 lumber board?

A nominal 2×4 is actually about 1.5 in × 3.5 in, or 38 mm × 89 mm. Nominal names are trade labels, not measured dimensions.

How do I convert feet and inches to millimetres for CNC files?

Convert the total inches first: feet × 12 plus remaining inches, then multiply by 25.4 mm/in. An 8′-6″ run is 102 in = 2,590.8 mm.

What is the difference between a mile and a nautical mile?

One statute mile is 1,609.34 m. One nautical mile is 1,852 m and is used for aviation and marine distance. They are not interchangeable.

How many metres are in a yard of fabric?

One yard equals 0.9144 m. Three yards is 2.743 m. Fabric priced per metre versus per yard needs conversion before comparing unit cost.

Why do blueprints mix imperial and metric on one drawing?

US projects often dimension in feet/inches while hardware and steel sections are specified in millimetres. Conversion is required at every interface detail.

Real-World Applications

📐

Blueprint Dimensions

Architectural drawings may show feet-and-inches while steel, glass, and CNC suppliers ask for millimetres. A small rounding mistake can turn into a fit problem on site.

🧵

Fabric and Textile Orders

US sewing patterns use yards and inches; many fabric sellers list metres and centimetres. Converting lengths prevents under-ordering after seam allowances are included.

🗺️

Survey and Deed Records

Older land records may use chains, rods, feet, or miles, while modern GIS systems use metres. Length conversion is the first step before calculating area boundaries.

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Nautical Distance Planning

Charts and vessel routes use nautical miles, not land miles. Converting route legs helps compare voyage distance with road or rail alternatives.

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Lumber and Workshop Setup

Woodworking plans mix nominal inches, actual dimensions, and metric hardware. Converting the measured length keeps cuts and fastener spacing aligned.

🔬

Microscope and Lab Scales

Lab notes move between micrometres, millimetres, and inches on equipment specs. Conversion keeps specimen sizes and instrument travel ranges comparable.

Length Conversion Mistakes to Avoid

Squaring a linear factor for area by accident

Because 1 m ≈ 3.281 ft, some multiply metres by 3.281 to get square feet. Area needs 3.281². Use the Area Converter for surface measurements.

Using nominal lumber sizes as exact inputs

Cutting steel or cabinetry to a nominal 2 in dimension without checking the actual 1.5 in finished size causes cumulative fit errors on long runs.

Dropping fractional inches too early

Rounding ⅜ in to 0.3 in before converting to millimetres shifts CNC toolpaths. Keep fractions exact through the conversion.

Confusing survey chains with feet

Older deeds may list chains or rods. One chain is 66 ft. Applying a metre conversion to the wrong unit invalidates boundary calculations.

Mixing nautical and statute miles on routes

A 100 nautical-mile flight leg is 115 statute miles. Fuel and time planning errors appear if the wrong mile type is used.

Length Unit Quick Reference

Unit	Exact Metres	Common Use
1 inch	0.0254 m	US/UK everyday measurement
1 foot	0.3048 m	US/UK height, altitude
1 yard	0.9144 m	US fabric, sports fields
1 mile	1,609.344 m	US/UK road distances
1 nautical mile	1,852 m	Navigation, aviation
1 light-year	9.461 × 10¹⁵ m	Astronomical distances

References

BIPM. The International System of Units (SI), 9th Edition. Bureau International des Poids et Mesures, 2019.
NIST. Metric System of Measurement — Interpretation of the International System of Units. Federal Register, 2008.
ISO 80000-3. Quantities and Units — Space and Time. ISO, 2019.
Cardarelli, François. Encyclopaedia of Scientific Units, Weights and Measures. Springer, 2003.
IUPAC. Quantities, Units and Symbols in Physical Chemistry. RSC Publishing, 2007.