How many centimeters are in an inch?

One inch equals exactly 2.54 centimeters. This is an exact mathematical relationship (defined in 1959 by international agreement). Multiplying or dividing by 2.54 converts perfectly between inches and centimeters. Common rounded conversions: 4 inches ≈ 10 cm (precise: 10.16); 6 inches ≈ 15 cm (precise: 15.24); 12 inches = 30.48 cm. For everyday use: 1 inch ≈ 2.5 cm mental shortcut. For precision: use full 2.54 conversion factor.

How many feet are in a meter?

One meter equals approximately 3.281 feet (precisely 3.28083989501). Or one foot equals 0.3048 meters exactly. For mental math: 1 m ≈ 3.3 feet, 1 foot ≈ 0.3 m. Common conversions: 5 feet = 1.52 m; 6 feet = 1.83 m; 10 feet = 3.05 m. Often rounded to convenient values: 5 feet ≈ 150 cm; 6 feet ≈ 180 cm. For body height: 5'10" ≈ 178 cm. Construction commonly: 2x4 = 5cm × 10cm approximation (actual: 38×89mm).

How many kilometers are in a mile?

One mile equals approximately 1.60934 kilometers. Or one kilometer equals approximately 0.62137 miles. For mental math: 1 mile ≈ 1.6 km, 1 km ≈ 0.6 miles. Common race distances: 5K = 3.1 miles; 10K = 6.2 miles; half marathon = 13.1 miles; marathon = 26.2 miles. Travel comparisons: 100 miles ≈ 160 km. Cycling century: 100 miles ≈ 160 km. Highway driving 60 mph ≈ 100 km/h.

What's the difference between meters and yards?

YARD: imperial unit, 3 feet = 36 inches = 0.9144 meters. METER: metric base unit, 100 cm = 39.37 inches. Difference: 1 meter is ~3.4 inches LONGER than 1 yard. Yards used in: American football (100-yard field), some construction, fabric/sewing. Meters used in: international sports (200m sprint), scientific work, most countries' daily measurements. Common confusion: "I ran a 100" might mean meters (international standard) or yards (American). Always specify when ambiguous. Conversion: 100 yards = 91.44 m; 100 meters = 109.4 yards.

How do I convert between metric units (mm, cm, m, km)?

Decimal-based metric system makes conversion simple: multiply or divide by powers of 10. MILLIMETERS × 10 = CENTIMETERS (move decimal one place right reading right-to-left). CENTIMETERS × 100 = METERS (move decimal two places). METERS × 1000 = KILOMETERS (move decimal three places). Examples: 50 mm = 5 cm = 0.05 m. 250 cm = 2.5 m = 0.0025 km. 1500 m = 1.5 km. Working backward: 7 km = 7000 m = 700,000 cm. No memorized factors needed. This is why metric system dominant in scientific/engineering use — calculation simplicity over imperial.

Length Converter

Convert any length or distance measurement between imperial and metric units. Supports inches, feet, yards, miles, millimeters, centimeters, meters, and kilometers with instant results.

Length conversion between imperial (inches, feet, yards, miles) and metric (millimeters, centimeters, meters, kilometers) systems is one of the most common everyday calculations. The US remains one of only three countries (US, Liberia, Myanmar) that hasn't officially adopted the metric system, creating constant need for conversion in international trade, scientific work, sports, travel, manufacturing, and engineering. Even within US contexts: medicine uses metric, science uses metric, manufacturing increasingly uses metric while consumer products use imperial.

The fundamental conversion factors: 1 inch = 2.54 cm (exact); 1 foot = 12 inches = 30.48 cm; 1 yard = 3 feet = 0.9144 meters; 1 mile = 1,760 yards = 1.609 km. Within metric system: 1 cm = 10 mm; 1 m = 100 cm; 1 km = 1,000 m. Decimal-based metric makes calculations dramatically simpler — multiplying or dividing by powers of 10. Imperial requires memorizing arbitrary multipliers (12, 3, 1,760) which causes common errors.

This calculator converts between any combination of length/distance units. Use it for: international communications, recipe conversions, athletic measurements, scientific work, travel planning, construction projects, or DIY tasks. Important context: precision matters for some applications (engineering, medicine), approximate is fine for others (informal conversation, casual planning). For mental conversion: 1 inch ≈ 2.5 cm, 1 foot ≈ 30 cm, 1 yard ≈ 1 meter, 1 mile ≈ 1.6 km. These rough approximations work for casual use. For precision: use exact conversion factors.

Inputs

Value

From Unit (0=in, 1=ft, 2=yd, 3=mi, 4=mm, 5=cm, 6=m, 7=km)

Results

Inches

39.3701

Feet

3.2808

Yards

1.0936

Miles

6.214e-4

Millimeters

1,000

Centimeters

100

Meters

Kilometers

0.001

Last updated: May 27, 2026

Formula

Standard length conversion factors: Imperial system: 1 foot = 12 inches 1 yard = 3 feet = 36 inches 1 mile = 1,760 yards = 5,280 feet 1 nautical mile = 6,076 feet (used for sea and air navigation) Metric system (decimal-based): 1 cm = 10 mm 1 m = 100 cm = 1,000 mm 1 km = 1,000 m 1 km = 100,000 cm = 1,000,000 mm Imperial to Metric conversions: 1 inch = 25.4 mm = 2.54 cm (exact) 1 foot = 304.8 mm = 30.48 cm (exact) 1 yard = 914.4 mm = 91.44 cm = 0.9144 m (exact) 1 mile = 1,609.344 meters = 1.609 km Metric to Imperial conversions: 1 mm = 0.03937 inches 1 cm = 0.3937 inches 1 m = 3.281 feet = 39.37 inches = 1.094 yards 1 km = 0.6214 miles = 1,094 yards = 3,281 feet Example conversions: 100 cm to inches: 100 / 2.54 = 39.37 inches 100 inches to cm: 100 × 2.54 = 254 cm 6 feet to meters: 6 × 0.3048 = 1.829 m 5 km to miles: 5 × 0.6214 = 3.107 miles 2 miles to km: 2 × 1.6093 = 3.219 km Common conversion needs: HEIGHT (human): 5 feet = 152 cm 5.5 feet (5'6") = 168 cm 6 feet = 183 cm 6'4" = 193 cm Average US adult male: 5'9" = 175 cm Average US adult female: 5'4" = 162 cm DISTANCE (running/cycling): 5K = 3.1 miles (popular short race distance) 10K = 6.2 miles Half marathon = 21.1 km = 13.1 miles Marathon = 42.2 km = 26.2 miles Century ride (cycling) = 100 miles = 160.9 km Tour de France daily stage average: 150 km = 93 miles PRACTICAL DISTANCES: 1 city block (US average): 0.05-0.10 miles = 80-160 m 1 football field (American): 120 yards = 110 m 1 country mile: typical "go ahead in mile" estimation 1 typical airport (small): 0.5-1 mile = 0.8-1.6 km 1 typical airport runway: 1.5-3 km = 1-1.9 miles SCIENTIFIC SCALES: Width of human hair: 0.07 mm = 0.0028 inches Period at end of sentence: 0.3 mm Standard credit card: 85.6 mm × 53.98 mm Standard letter paper US: 8.5" × 11" = 216 × 279 mm A4 paper: 210 mm × 297 mm = 8.27" × 11.7" Standard nail: 1-3 inches = 25-75 mm Standard pencil: 7 inches = 178 mm Earth's diameter: 7,917.5 mi = 12,742 km Distance to Moon: 238,855 mi = 384,400 km ENGINEERING/MANUFACTURING: Tolerances often in mm or fractions of an inch Common machine tolerances: ±0.001 inch = ±0.025 mm Sub-mm tolerances common in precision manufacturing Thread sizes (US standard): UNC, UNF Metric thread: M5, M6, M8, M10, M12 (diameter in mm) CONSTRUCTION: Standard 2x4 lumber: actually 1.5 × 3.5 inches (38 × 89 mm) Standard 4x8 plywood: 4 ft × 8 ft (1.22 × 2.44 m) Standard door: 30-36 in wide (76-91 cm) Wall stud spacing US: 16 inches on-center (40.6 cm) Common ceiling height: 8-9 ft (2.44-2.74 m) ROAD INFRASTRUCTURE: Standard lane width US: 12 ft (3.66 m) Standard parking space: 9 × 18 ft (2.74 × 5.49 m) Highway speed limit signs in mph (US); km/h (most other countries) Conversion mental shortcuts: For quick mental conversions: - 1 mile ≈ 1.6 km (precise: 1.6093) - 1 km ≈ 0.6 mi (precise: 0.6214) - 1 m ≈ 39 inches (precise: 39.37) - 1 foot ≈ 30 cm (precise: 30.48) - 1 yard ≈ 0.9 m (precise: 0.9144) - 1 inch = exactly 2.54 cm - 10 cm = nearly 4 inches (precise: 3.94) Decimal conversions in head: - mph × 1.6 = km/h (approximate) - km/h × 0.625 = mph - inches × 2.5 + 10% = cm - cm × 0.4 = inches (approximate) For scientific accuracy: use full decimal precision; calculators or tables. International contexts: US: - Daily: imperial (inches, feet, miles, yards) - Scientific: metric - Medical: metric (height in cm, weight in kg often) - Sports: imperial mostly; some events metric (5K, 10K racing) UK: - Mixed system - Distances on road: miles (km on some) - Heights: feet and inches commonly - Liquid: pints (different than US pint!) EU/Most world: - Metric standard - Some traditional units retained (square meter common but hectare also used) Conversion accuracy needs: EXACT (engineering, scientific): Use full conversion: 1 in = 25.4 mm precisely REASONABLE (most everyday): 2-3 significant figures sufficient 1 mile ≈ 1.6 km is fine for casual use APPROXIMATION (mental math): Less precise but quick Useful for travel planning, casual reference For programming/calculation: always use precise conversion factors. For manual estimation: round factors acceptable. Common conversion mistakes: CONFUSING DECIMAL POINTS: - 1.5 inches vs. 1,5 inches (European thousands) - Some European countries use comma as decimal VOLUME vs. LENGTH: - Cubic feet vs. feet - Conversions different (volume: factor cubed) PRECISION CONFUSION: - 1 mile = 1.6 km (common) vs. 1.6093 km (precise) - Each works for different uses FRACTIONS vs. DECIMALS: - 1/4 inch = 0.25 inches = 6.35 mm - 3/8 inch = 0.375 inches = 9.525 mm - Imperial fractions confuse non-imperial users UNIT NOTATION: - "in" vs. "ft" abbreviations - Mixed unit notation: 5'10" (5 feet 10 inches) - Different formats internationally

How to use this calculator

Enter the value to convert.
Select source unit from dropdown.
Review automatic conversions across all length units.
For mental math: 1 inch = 2.54 cm (exact); 1 foot ≈ 30 cm; 1 mile ≈ 1.6 km.
For precision use: use full decimal places shown.
For everyday conversation: round to 1-2 significant figures.
For programming: store conversion factors at full precision.
For international communications: state units explicitly to avoid confusion.
For sports: 5K = 3.1 miles, half marathon = 13.1 miles, marathon = 26.2 miles.
For travel: 1 mile = 1.6 km approximation.
For body measurements: 5'10" = 178 cm typically rounded.
For engineering: use exact conversion (1" = 25.4mm).

Worked examples

Recipe height conversion

Recipe says cake should be 25 cm diameter. Convert to inches. 25 cm × 0.3937 = 9.84 inches Or: 25 / 2.54 = 9.84 inches Round to nearest practical size: 10 inches (close enough). Common cake pan sizes: 8 inch = 20 cm 9 inch = 23 cm 10 inch = 25 cm 11 inch = 28 cm A 10-inch pan would work fine for a 25 cm recipe. International recipes use cm for cake pans, oz/grams for ingredients. Converting requires understanding both systems.

Travel distance comparison

Driving 250 miles in US. Same trip in km? 250 miles × 1.609 = 402 km Or rough mental math: 250 × 1.6 = 400 km (close enough). European driver looking at same drive: would estimate 4-5 hours at typical 80 km/h highway speed. US driver: same drive at 60-70 mph = 3.5-4 hours. Different speeds, similar travel times. Same distance: New York to Washington DC ≈ 380 km = 236 miles. European reference: London to Manchester ≈ 320 km = 199 miles. International road trip planners need this conversion constantly.

Height conversion

Person's height 6'2" (six feet two inches) in cm. Method 1: Convert each part 6 feet = 6 × 12 = 72 inches 6'2" = 74 inches 74 × 2.54 = 188 cm Method 2: Direct 6.167 feet × 30.48 = 188 cm Same answer: 188 cm. Common height conversions: 5'0" = 152 cm 5'4" = 162 cm 5'8" = 172 cm 6'0" = 183 cm 6'4" = 193 cm For medical records, international applications, drivers licenses outside US: metric height standard. Many people memorize their own height in both systems.

When to use this calculator

Use this calculator for international communications, recipe conversions, athletic measurements, scientific work, travel planning, construction projects, DIY tasks, or any imperial-metric conversion need.

Pair with weight-converter, speed-converter, and temperature-converter.

Important conversion considerations:

1. **1 inch = 2.54 cm exactly.** This is the foundational US-metric conversion.

2. **Imperial vs. metric varies by application.** US daily life imperial; science/medicine metric; manufacturing increasingly metric.

3. **Approximation often sufficient.** 1 mile ≈ 1.6 km close enough for casual use.

4. **Precision matters for engineering.** Use full conversion: 1 inch = 25.4 mm.

5. **Some countries use both.** UK uses miles on road signs but km for distances in many contexts.

6. **Decimal vs. fractional notation.** Imperial uses fractions (1/4 inch); metric uses decimals.

7. **Different countries different decimal markers.** US uses "." for decimal; many EU countries use ",".

8. **Sports often follow metric.** International athletic events use meters and km (5K, 10K, marathon).

9. **Body measurements vary by region.** US: feet/inches; everywhere else mostly: cm.

10. **Construction units vary.** US lumber/buildings in feet/inches; Europe in mm/cm.

11. **Volume separate.** Cubic feet vs. cubic meters not the same as feet vs. meters (factor cubed).

12. **Manufacturing tolerances precise.** ±0.001" or ±0.025 mm typical machining precision.

Common mistakes to avoid

Using approximate conversions for engineering. ±0.1 mm tolerance requires precise factor 25.4.
Confusing cubic and linear units. Cubic feet to cubic meters very different from feet to meters.
Mixing decimal notation styles. US "." vs. European "," can confuse data.
Forgetting fraction conversions. 1/4 inch = 6.35 mm exactly.
Using rough estimates when precision matters. Use exact factor when accuracy required.
Wrong direction multiplication. mph × 1.6 = km/h, not divide.

Frequently Asked Questions

Sources & further reading

National Institute of Standards Conversion — U.S. National Institute of Standards and Technology
International System of Units — International Bureau of Weights and Measures (BIPM)
Metric System Resources — International Organization for Standardization

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