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Unit converter

A free unit converter for length, weight, temperature, volume, area, speed, data and time: converted instantly, with the whole table of equivalents so you never have to do it twice.

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6.2137119

1 kilometre = 0.62137119 milescontent_copyCopy result

10km in every unit

Millimetre10,000,000 mmCentimetre1,000,000 cmMetre10,000 mKilometre10 kmInch393,700.79 inFoot32,808.399 ftYard10,936.133 ydMile6.2137119 miNautical mile5.399568 nmi

~/make-it-real

How big is 10 km?

Numbers are easier to picture next to familiar things. Your value, compared:

directions_walkA typical stride0.00075 km× 13,333.3

sports_soccerA football pitch0.105 km× 95.2

apartmentEiffel Tower height0.33 km× 30.3

directions_runA marathon42.195 km23.7% of it

~/do-it-in-your-head

Rules of thumb worth remembering.

Close enough for everyday use, the exact factor is shown so you know how far off you are.

Kilometres to mileskm × 0.610 km ≈ 6 miles (a 10K run)exact: 0.6214±3.5%

Kilograms to poundskg × 2.270 kg ≈ 154 lbexact: 2.2046±0.2%

Celsius to Fahrenheit°C × 2 + 3020 °C ≈ 70 °F (exact: 68)exact: × 1.8 + 32±~3° near room temp

Inches to centimetresin × 2.512 in ≈ 30 cmexact: 2.54±1.6%

Litres to US gallonsL ÷ 440 L ≈ 10 gallonsexact: ÷ 3.785±5.4%

Metres to feetm × 3.32 m ≈ 6.6 ftexact: 3.2808±0.6%

~/two-systems

Why there are two systems.

The metric system scales in tens, 1,000 metres in a kilometre, 1,000 grams in a kilogram, so converting within it is just moving a decimal point. Imperial and US units grew from everyday objects, which is why a foot has 12 inches and a mile has 5,280 feet.

Watch out for units that share a name but not a size: a US gallon is smaller than a UK gallon, and a US ton is lighter than a metric tonne.

US gallon3.785 litres≠UK gallon4.546 litres

US ton907 kg≠Metric tonne1,000 kg

Gigabyte (GB)1,000,000,000 bytes≠Gibibyte (GiB)1,073,741,824 bytes

US cup237 ml≠Metric cup250 ml

~/exact-by-definition

Most conversion factors are exact. Computers still round them.

Since 1959 the inch has been exactly 25.4 mm and the pound exactly 0.453 592 37 kg, so every imperial unit has an exact value in SI. This lab reruns your conversion from the converter above in exact fraction arithmetic. It shows the full answer, whether its decimals ever end, and how far the browser’s 64-bit floating-point result is from it.

10 km → mi1 mi → km100 °F → °C1 cup → ml1 acre → m²60 mph → km/h

10 km → mi, exactly

from · km1 km = 1000 mSI prefix

to · mi1 mi = 5280 ft = 63 360 × 0.0254 m = 1609.344 m1959 agreement

exact result as a fraction78125 / 12573

exact decimal (first 48 digits, repeats)6.213711922373339696174341843633182215859381213711…

exact6.21371192237333969617434184363318221585…

64-bit double6.2137119223733395

shown above6.2137119

relative error of the double3.66e-17Error introduced by rounding inside the calculation.

error in ULPs0.26Units in the last place of the result. Under 0.5 means correctly rounded.

1,000 round tripsno driftConverting km → mi → km a thousand times with doubles.

denominator12,573Of the reduced fraction. Only 2s and 5s give a terminating decimal.

check_circleIt never ends. The block “213711922373339696174341…” repeats forever (period 42), because the denominator has prime factors other than 2 and 5.

~/where-the-metre-comes-from

Seven fixed numbers define every unit.

Since 20 May 2019, the SI has no physical prototypes. Seven constants of nature were given exact values, and each base unit is derived from them. The matrix shows the power of each constant in each unit; the coefficients are computed live from the exact values and checked against the BIPM’s SI Brochure. Click a unit for its derivation, or a constant to see what depends on it.

unitΔνCschekNAKcdcoefficient (computed · brochure)

seconds · time−1······9.19263177e+9check_circle9.1926318e+9 matches

metrem · length−1+1·····30.6633190check_circle30.663319 matches

kilogramkg · mass+1−2+1····1.47552140e+40check_circle1.4755214e+40 matches

ampereA · electric current+1··+1···678968682check_circle6.7896868e+8 matches

kelvinK · temperature+1·+1·−1··2.26666526check_circle2.2666653 matches

molemol · amount of substance·····−1·6.02214076e+23check_circle6.0221408e+23 matches

candelacd · luminous intensity+2·+1···+12.61483048e+10check_circle2.6148305e+10 matches

kilogram (kg), masskg = (299 792 458² / (6.626 070 15×10⁻³⁴ × 9 192 631 770)) h ΔνCs / c²Fixing h means a Kibble balance, which compares mechanical and electrical power, can realise the kilogram anywhere without a reference mass.

before 2019From 1889 to 2019, the mass of the International Prototype of the Kilogram, a platinum-iridium cylinder kept near Paris. Its official copies drifted by about 50 micrograms over a century.

The seven defining constants (exact)

ΔνCs9 192 631 770 Hzcaesium-133 hyperfine frequency

c299 792 458 m/sspeed of light in vacuum

h6.626 070 15 × 10⁻³⁴ J sPlanck constant

e1.602 176 634 × 10⁻¹⁹ Celementary charge

k1.380 649 × 10⁻²³ J/KBoltzmann constant

NA6.022 140 76 × 10²³ mol⁻¹Avogadro constant

Kcd683 lm/Wluminous efficacy of 540 THz light

~/where-did-my-gigabytes-go

One drive, four different sizes on screen.

Drive makers use SI prefixes: 1 GB is 10⁹ bytes. Windows divides by 2³⁰ and still writes “GB”. macOS switched to decimal in 2009, and Linux tools offer both. No bytes go missing; the same number is divided by a different power. The IEC binary prefixes (KiB, MiB, GiB) exist to remove the ambiguity.

1 TB SSD500 GB drive128 GB phone4.7 GB DVD1.44 MB floppy20 TB disk

Size on the box

bytes1,000,000,000,000

Download speed (megabits per second)

time to download it22 h 13 min8,000,000,000,000 bits ÷ 100,000,000 bits/s. Network speeds use decimal megabits; divide by 8 for megabytes per second (12.5 MB/s). Protocol overhead adds roughly 3-10%.

On the boxbytes ÷ 1000ⁿ, labelled GB1 TBDrive makers, and the SI and IEC standards.

macOS Finderbytes ÷ 1000ⁿ, since 10.6 (2009)1 TBMatches the box.

Windows File Explorerbytes ÷ 1024ⁿ, labelled GB931 GBLooks 9.1% smaller than the box. The unit is really GiB.

Linux df -hbytes ÷ 1024ⁿ, rounded up932GGNU coreutils rounds up so free space is never overstated.

Linux df -Hbytes ÷ 1000ⁿ, rounded up1.0TThe SI option.

IEC unambiguousbytes ÷ 1024ⁿ, labelled GiB931.32 GiBWhat Windows means but does not write.

storageThis browser offers this site 10.74 GB (10.00 GiB) of storage, with 0 bytes used. Reported by navigator.storage.estimate(), always in bytes.

KiBvs kB2^10 = 1,024+2.4% larger

MiBvs MB2^20 = 1,048,576+4.9% larger

GiBvs GB2^30 = 1,073,741,824+7.4% larger

TiBvs TB2^40 = 1,099,511,627,776+10.0% larger

PiBvs PB2^50 = 1,125,899,906,842,624+12.6% larger

EiBvs EB2^60 = 1,152,921,504,606,846,976+15.3% larger

ZiBvs ZB2^70 = 1,180,591,620,717,411,303,424+18.1% larger

YiBvs YB2^80 = 1,208,925,819,614,629,174,706,176+20.9% larger

~/reference

Legal definitions of everyday units.

Each value is exact by law or treaty. The converter above uses these factors.

unitdefined asexact SI valueset by

inch25.4 mm0.0254 mInternational yard and pound agreement, 1959

foot12 inches0.3048 m1959 agreement

US survey foot1200/3937 m0.304 800 609 601 2… mMendenhall Order 1893; deprecated 31 Dec 2022

yard3 feet0.9144 m1959 agreement

mile5280 feet1609.344 m1959 agreement

nautical mile1852 m1852 mInternational Hydrographic Conference, Monaco, 1929

pound0.453 592 37 kg0.45359237 kg1959 agreement

ounce (avoirdupois)1/16 pound0.028349523125 kg1959 agreement

stone14 pounds6.35029318 kgUK Weights and Measures Act 1985

metric carat200 mg0.0002 kg4th CGPM, 1907

litre1 dm³0.001 m³12th CGPM, 1964 (1901-1964: volume of 1 kg of water)

US gallon231 cubic inches0.003785411784 m³Wine gallon of 1707, with the 1959 inch

UK gallon4.546 09 litres0.00454609 m³UK Weights and Measures Act 1985

acre43 560 square feet4046.8564224 m²1959 agreement

The US survey foot is 2 parts per million longer than the international foot. Over a survey mile that comes to exactly 6 336 000/3937 − 1609.344 = 3.2187 mm, computed in exact fractions, enough to misplace state-plane coordinates by metres. NIST deprecated it from 1 January 2023.