Length Converter – Convert mm, cm, m, km, Inches, Feet, Yards & Miles Online
Instant length conversion between metric and imperial units — plus conversion charts, formula cheat sheet, and quick-conversion cards for popular pairs
Result
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Quick Length Conversions – Most Popular Pairs
The Metric Length System – km, m, cm, mm Explained
The metric system uses powers of 10, making conversions simple multiplications or divisions. Here is the full length hierarchy from largest to smallest:
Kilometer (km)= 1,000 m = 100,000 cm = 1,000,000 mm
▼ ÷ 1,000
Meter (m)= 100 cm = 1,000 mm = 0.001 km
▼ ÷ 100
Centimeter (cm)= 10 mm = 0.01 m = 0.00001 km
▼ ÷ 10
Millimeter (mm)= 0.1 cm = 0.001 m = 0.000001 km
▼ ÷ 1,000
Micrometer (μm)= 0.001 mm = 0.0001 cm (used in science/engineering)
To convert down (to a smaller unit), multiply. To convert up (to a larger unit), divide.
Length Conversion Chart – Metric and Imperial
Metric units: common values
| mm | cm | m | km |
|---|---|---|---|
| 1 mm | 0.1 cm | 0.001 m | 0.000001 km |
| 10 mm | 1 cm | 0.01 m | 0.00001 km |
| 100 mm | 10 cm | 0.1 m | 0.0001 km |
| 1,000 mm | 100 cm | 1 m | 0.001 km |
| 10,000 mm | 1,000 cm | 10 m | 0.01 km |
| 100,000 mm | 10,000 cm | 100 m | 0.1 km |
| 1,000,000 mm | 100,000 cm | 1,000 m | 1 km |
Imperial / customary units: common values
| Inches (in) | Feet (ft) | Yards (yd) | Miles (mi) |
|---|---|---|---|
| 1 in | 0.0833 ft (1/12) | 0.0278 yd | 0.0000158 mi |
| 12 in | 1 ft | 0.333 yd | 0.000189 mi |
| 36 in | 3 ft | 1 yd | 0.000568 mi |
| 63,360 in | 5,280 ft | 1,760 yd | 1 mi |
Metric to imperial: key reference values
| Metric | Inches | Feet | Yards | Miles |
|---|---|---|---|---|
| 1 mm | 0.03937 in | 0.003281 ft | 0.001094 yd | — |
| 1 cm | 0.3937 in | 0.03281 ft | 0.01094 yd | — |
| 10 cm | 3.937 in | 0.3281 ft | 0.1094 yd | — |
| 30.48 cm | 12 in | 1 ft | 0.333 yd | — |
| 1 m | 39.37 in | 3.2808 ft | 1.0936 yd | 0.000621 mi |
| 100 m | 3,937 in | 328.08 ft | 109.36 yd | 0.0621 mi |
| 1 km | 39,370 in | 3,280.8 ft | 1,093.6 yd | 0.6214 mi |
| 1.609 km | 63,360 in | 5,280 ft | 1,760 yd | 1 mi |
Imperial to metric: key reference values
| Imperial | mm | cm | m | km |
|---|---|---|---|---|
| 1 inch | 25.4 mm | 2.54 cm | 0.0254 m | — |
| 1 foot | 304.8 mm | 30.48 cm | 0.3048 m | 0.000305 km |
| 1 yard | 914.4 mm | 91.44 cm | 0.9144 m | 0.000914 km |
| 1 mile | 1,609,344 mm | 160,934 cm | 1,609.344 m | 1.609344 km |
Length Units Reference Table
| Unit | Symbol | System | Value in Meters | Common Use |
|---|---|---|---|---|
| Nanometer | nm | Metric | 0.000000001 m (10⁻⁹) | Atomic/molecular scale, light wavelengths |
| Micrometer | μm | Metric | 0.000001 m (10⁻⁶) | Bacteria size, engineering tolerances |
| Millimeter | mm | Metric | 0.001 m | Ruler measurements, rainfall, product specs |
| Centimeter | cm | Metric | 0.01 m | Body measurements, clothing, screen sizes |
| Decimeter | dm | Metric | 0.1 m | Rarely used; academic reference |
| Meter | m | Metric | 1 m (base unit) | Room dimensions, building heights, athletics |
| Kilometer | km | Metric | 1,000 m | Road distances, maps, geography |
| Inch | in | Imperial | 0.0254 m | Screen sizes, shoe sizes, US construction |
| Foot | ft | Imperial | 0.3048 m | Height, US construction, floor plans |
| Yard | yd | Imperial | 0.9144 m | American football, fabric, US landscaping |
| Mile | mi | Imperial | 1,609.344 m | Road distances in US and UK |
| Nautical Mile | nmi | Navigation | 1,852 m | Maritime and aviation navigation |
Length Conversion Formula Cheat Sheet
ft → m
m = ft × 0.3048
6 ft = 6 × 0.3048 = 1.8288 m
m → ft
ft = m × 3.28084
2 m = 2 × 3.28084 = 6.562 ft
in → cm
cm = in × 2.54
10 in = 10 × 2.54 = 25.4 cm
cm → in
in = cm ÷ 2.54
30 cm = 30 ÷ 2.54 = 11.81 in
mm → cm
cm = mm ÷ 10
350 mm = 350 ÷ 10 = 35 cm
cm → mm
mm = cm × 10
8.5 cm = 8.5 × 10 = 85 mm
mm → m
m = mm ÷ 1000
2500 mm = 2500 ÷ 1000 = 2.5 m
km → mm
mm = km × 1,000,000
3 km = 3,000,000 mm
mm → km
km = mm ÷ 1,000,000
5,000,000 mm = 5 km
ft → yd
yd = ft ÷ 3
15 ft = 15 ÷ 3 = 5 yd
ft → km
km = ft × 0.0003048
5280 ft = 1.609 km (1 mile)
mi → km
km = mi × 1.60934
10 mi = 16.09 km
km → mi
mi = km × 0.62137
100 km = 62.14 mi
mm → in
in = mm ÷ 25.4
50 mm = 50 ÷ 25.4 = 1.969 in
ft → mm
mm = ft × 304.8
4 ft = 4 × 304.8 = 1219.2 mm
m → km
km = m ÷ 1000
3500 m = 3.5 km
Worked Examples
Example 1 – 250 mm to cm
Formula: cm = mm ÷ 10
Step 1: 250 ÷ 10 = 25 cm
Moving from mm to cm means dividing by 10. This is equivalent to moving one step up the metric ladder.
Step 1: 250 ÷ 10 = 25 cm
Moving from mm to cm means dividing by 10. This is equivalent to moving one step up the metric ladder.
Example 2 – 1800 mm to m
Formula: m = mm ÷ 1000
Step 1: 1800 ÷ 1000 = 1.8 m
1800 mm is a common door height in residential construction — equivalent to 1.8 meters or about 5 ft 11 in.
Step 1: 1800 ÷ 1000 = 1.8 m
1800 mm is a common door height in residential construction — equivalent to 1.8 meters or about 5 ft 11 in.
Example 3 – 5 km to mm
Formula: mm = km × 1,000,000
Step 1: 5 × 1,000,000 = 5,000,000 mm
Going from km to mm crosses three metric steps: km → m (×1000), m → cm (×100), cm → mm (×10). Combined: ×1,000,000.
Step 1: 5 × 1,000,000 = 5,000,000 mm
Going from km to mm crosses three metric steps: km → m (×1000), m → cm (×100), cm → mm (×10). Combined: ×1,000,000.
Example 4 – 12 ft to m
Formula: m = ft × 0.3048
Step 1: 12 × 0.3048 = 3.6576 m
12 feet is a common ceiling height in commercial buildings — approximately 3.66 meters.
Step 1: 12 × 0.3048 = 3.6576 m
12 feet is a common ceiling height in commercial buildings — approximately 3.66 meters.
Example 5 – 6 ft to yards
Formula: yd = ft ÷ 3
Step 1: 6 ÷ 3 = 2 yards
There are exactly 3 feet in 1 yard. This is one of the most reliable imperial conversions to memorize.
Step 1: 6 ÷ 3 = 2 yards
There are exactly 3 feet in 1 yard. This is one of the most reliable imperial conversions to memorize.
Example 6 – 24.5 cm to inches (shoe size)
Formula: in = cm ÷ 2.54
Step 1: 24.5 ÷ 2.54 = 9.646 inches
24.5 cm is a common shoe size equivalent to approximately US men's size 7 / women's size 8.5. The exact conversion is 9.646 inches or about 9 and 5/8 inches.
Step 1: 24.5 ÷ 2.54 = 9.646 inches
24.5 cm is a common shoe size equivalent to approximately US men's size 7 / women's size 8.5. The exact conversion is 9.646 inches or about 9 and 5/8 inches.
Example 7 – 1000 mm to feet
Formula: ft = mm ÷ 304.8
Step 1: mm → m: 1000 ÷ 1000 = 1 m
Step 2: m → ft: 1 × 3.28084 = 3.281 ft
1000 mm = 1 meter = approximately 3 feet 3.4 inches. A common conversion in construction and engineering.
Step 1: mm → m: 1000 ÷ 1000 = 1 m
Step 2: m → ft: 1 × 3.28084 = 3.281 ft
1000 mm = 1 meter = approximately 3 feet 3.4 inches. A common conversion in construction and engineering.
Example 8 – 2.5 m to feet
Formula: ft = m × 3.28084
Step 1: 2.5 × 3.28084 = 8.202 ft
A ceiling height of 2.5 m is approximately 8 feet 2.4 inches — standard in many modern residential builds.
Step 1: 2.5 × 3.28084 = 8.202 ft
A ceiling height of 2.5 m is approximately 8 feet 2.4 inches — standard in many modern residential builds.
Metric vs Imperial Length Units – When to Use Each
Metric system (mm, cm, m, km)
Metric units are used by most of the world and by all scientific and engineering disciplines. Conversions are always powers of 10, making calculations fast and error-resistant. Key uses:
- mm: engineering tolerances, rainfall, product dimensions
- cm: body measurements, clothing sizes, short distances
- m: room dimensions, building heights, athletic distances
- km: road distances, geography, navigation (outside the US)
Imperial / US customary system (in, ft, yd, mi)
Imperial units are primarily used in the United States for everyday measurements, and in the UK for road distances (miles). The relationships between units are less regular — 12 inches per foot, 3 feet per yard, 1,760 yards per mile — making conversions require fixed factors rather than simple powers of 10.
- inch: screen sizes (TVs, monitors), shoe sizes, small measurements
- foot: human height, room dimensions, US construction
- yard: American football fields, fabric, US landscaping
- mile: US and UK road distances, running races
Converting Dimensions – Length, Width & Height
Important: This tool converts linear (one-dimensional) length values only. Converting length and width to area (square feet, square meters) is a different operation — use the Area Converter for that purpose.
To convert a 3D set of dimensions — for example, a room measured as 12 ft × 10 ft × 8 ft — convert each dimension individually:
- 12 ft × 0.3048 = 3.658 m
- 10 ft × 0.3048 = 3.048 m
- 8 ft × 0.3048 = 2.438 m
To find area (square feet to square meters): multiply each dimension's conversion factor by itself. Since 1 ft = 0.3048 m, 1 sq ft = 0.3048² = 0.0929 m². To find volume (cubic feet to cubic meters), use 0.3048³ = 0.02832 m³. These are area and volume conversions — use the dedicated Area Converter and Volume Calculator linked below.
Special Use Cases
Shoe size conversions (cm to inches)
Shoe sizes in many countries are listed in centimeters (the foot length). To convert to inches, divide by 2.54:
- 23 cm = 9.06 in (approx. US women's 6 / men's 5)
- 24.5 cm = 9.65 in (approx. US women's 8.5 / men's 7)
- 26 cm = 10.24 in (approx. US women's 10.5 / men's 8.5)
- 28 cm = 11.02 in (approx. US men's 10)
What does 1 cm look like in real size?
1 centimeter is approximately the width of your fingernail, or the diameter of a standard pen cap. On a standard monitor at 96 DPI, 1 cm ≈ 38 pixels. In the physical world: 1 cm = 10 mm = roughly 0.39 inches.
Construction and engineering
Construction projects often require converting between metric and imperial. Common references: standard lumber is 2×4 inches (38mm × 89mm actual size), door heights are typically 2032 mm (80 inches, 6 ft 8 in), and standard ceiling heights range from 2438 mm (8 ft) to 3048 mm (10 ft).
Classroom and homework
Common student conversions: 1 meter to feet (3.281 ft), 1 inch to cm (2.54 cm), km to miles (1 km = 0.621 mi), and the metric prefix ladder (kilo-, hecto-, deca-, base, deci-, centi-, milli-). Use the metric ladder diagram above as a quick study reference.
Common Length Conversion Mistakes
- Mixing linear units with square or cubic units. Converting 10 ft to meters gives 3.048 m (linear). Converting 10 sq ft to square meters requires multiplying by 0.0929 — a completely different factor. Length, area, and volume conversions are not interchangeable.
- Confusing mm and cm. Millimeters and centimeters differ by a factor of 10. 250 mm ≠ 250 cm. Always check: 1 cm = 10 mm.
- Forgetting feet and inches are separate. A height of 5 ft 9 in is not 5.9 feet — it's 5 + 9/12 = 5.75 feet. Convert feet and inches separately, then combine.
- Rounding too early in multi-step conversions. In km → mm conversions, rounding intermediate steps introduces compounding errors. Keep full precision until the final step.
- Confusing metric prefixes. Milli- = ÷1000 (millimeter = 1/1000 meter). Centi- = ÷100. Kilo- = ×1000. Mixing these up — especially milli- and centi- — causes 10× errors.
- Using 1 mile ≈ 1.6 km as exact. The exact value is 1 mile = 1.609344 km. For rough estimates, 1.6 km is fine; for precise engineering or navigation, use the full value.
Frequently Asked Questions
How do I convert ft to m?
Multiply feet by 0.3048. Formula: m = ft × 0.3048. Example: 10 ft = 10 × 0.3048 = 3.048 m. Use the quick ft → m card above for instant conversion.
How do I convert mm to cm?
Divide millimeters by 10. Formula: cm = mm ÷ 10. Example: 75 mm = 75 ÷ 10 = 7.5 cm. To reverse: cm × 10 = mm.
What is the length conversion formula?
All unit conversions use the meter as the base. Formula: Result = Input × (meters per From-unit) ÷ (meters per To-unit). Every unit has a fixed "meters per unit" factor. For example, 1 ft = 0.3048 m; 1 km = 1000 m. To convert 3 km to feet: 3 × 1000 ÷ 0.3048 = 9842.5 ft.
What is the difference between metric and imperial length units?
Metric units (mm, cm, m, km) are based on powers of 10 — easy to convert. Imperial/customary units (inch, foot, yard, mile) use irregular ratios: 12 inches per foot, 3 feet per yard, 1760 yards per mile. Metric is the global scientific standard; imperial is primarily used in the US for everyday measurement.
How many mm are in 1 km?
1 km = 1,000,000 mm (one million millimeters). The path: 1 km = 1000 m; 1 m = 1000 mm; therefore 1 km = 1000 × 1000 = 1,000,000 mm.
How many cm are in 1 inch?
Exactly 2.54 centimeters per inch (by international definition since 1959). Conversely, 1 cm = 1 ÷ 2.54 ≈ 0.3937 inches.
Can I convert length online for free?
Yes. The Length Converter above handles all common metric and imperial units instantly with no sign-up required. Use the main converter for any unit pair, or the quick-conversion cards for the most common pairs.
What is a length conversion chart?
A length conversion chart is a reference table showing equivalent values across different units. The charts above include metric-only, imperial-only, metric-to-imperial, and imperial-to-metric reference tables for common values.
How do I convert feet to yards?
Divide feet by 3. Formula: yd = ft ÷ 3. Example: 18 ft = 18 ÷ 3 = 6 yd. Reverse: yd × 3 = ft. There are exactly 3 feet in 1 yard.
How do I convert km to mm?
Multiply km by 1,000,000. Formula: mm = km × 1,000,000. Example: 0.5 km = 500,000 mm. The quick km → mm card above calculates this instantly.
How many inches is 24.5 cm?
24.5 cm ÷ 2.54 = 9.646 inches (approximately 9 and 5/8 inches). This is a common shoe-size calculation: 24.5 cm corresponds roughly to a US men's size 7 or women's size 8.5.
Can I convert dimensions here?
Yes for linear dimensions (length, width, height individually). Convert each dimension using the main converter. For area (length × width in square feet/meters), use the Area Converter. This tool handles one-dimensional linear measurements only.
What is the metric length system?
The metric system organizes length in powers of 10: 1 km = 1000 m; 1 m = 100 cm; 1 cm = 10 mm. Prefix kilo- means ×1000, centi- means ÷100, milli- means ÷1000. See the metric ladder diagram above for a visual overview.
How do I convert cm to inches?
Divide centimeters by 2.54. Formula: inches = cm ÷ 2.54. Example: 100 cm = 100 ÷ 2.54 ≈ 39.37 inches. Use the quick cm → inches card for instant answers.
How do I convert meters to feet?
Multiply meters by 3.28084. Formula: ft = m × 3.28084. Example: 1.75 m = 1.75 × 3.28084 = 5.74 ft (approximately 5 ft 8.9 in). Use the quick m → ft card for immediate results.
Related Calculators
Disclaimer: All conversions use internationally defined exact factors (e.g., 1 inch = 2.54 cm exactly; 1 foot = 0.3048 m exactly). Results are accurate to the precision selected. For mission-critical engineering, construction, or scientific measurements, verify results against certified reference standards. Area and volume conversions use different factors from linear length conversions — do not apply length conversion factors to square or cubic measurements.
