1kg with creditcard.JPG
Domestic-quality one-kilogram cast iron weight, shaped in accordance with OIML recommendation R52 for cast-iron hexagonal weights,[1] alongside a credit card for scale
Unit information
Unit systemSI base unit
Unit ofmass
Unit conversions
1 kg in ...... is equal to ...
   Avoirdupois   ≈ 2.205 pounds[Note 1]
   British Gravitational   ≈ 0.0685 slugs

The kilogram or kilogramme (symbol: kg) is the base unit of mass in the International System of Units (SI), and is defined as being equal to the mass of the International Prototype of the Kilogram (IPK, also known as "Le Grand K" or "Big K"),[2] a cylinder of platinum-iridium alloy stored by the International Bureau of Weights and Measures at Saint-Cloud, France.

The kilogram was originally defined as the mass of a litre (cubic decimetre) of water at its freezing point. That was an inconvenient quantity to precisely replicate, so in the late 18th century a platinum artefact was fashioned as a standard for the kilogram. That artefact, or an exact replica thereof, has been the standard of the unit of mass for the metric system ever since.

Though the IPK, the current primary artefact, and its replicas are stored in carefully controlled laboratory conditions, their masses have been subject to fluctuation as a result of poorly understood factors, possibly including handling, cleaning and contamination. The IPK has diverged from its replicas by 50 μg since their manufacture late in the 19th century. This has led to calls to replace the artefact with a standard defined in terms of invariant constants of nature.

The avoirdupois (or international) pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg,[3]making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are now also defined in terms of the kilogram, making the IPK the primary standard for virtually all units of mass on Earth.


The gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimetre of water at the melting point of ice.[4] The final kilogram, manufactured as a prototype in 1799 and from which the International Prototype Kilogram (IPK) was derived in 1875, had a mass equal to the mass of 1 dm3 of water under atmospheric pressure and at the temperature of its maximum density, which is approximately 4 °C.

The kilogram is the only named SI unit with an SI prefix (kilo) as part of its name. It is also the only SI unit that is still directly defined by an artefact rather than a fundamental physical property that can be independently reproduced in different laboratories. Three other base units (cd, A, mol) and 17 derived units (N, Pa, J, W, C, V, F, Ω, S, Wb, T, H, kat, Gy, Sv, lm, lx) in the SI system are defined in relation to the kilogram, and thus its stability is important. The definitions of only eight other named SI units do not depend on the kilogram: those of temperature (K, °C), time and frequency (s, Hz, Bq), length (m), and angle (rad, sr).[5]

The IPK is rarely used or handled. Copies of the IPK kept by national metrology laboratories around the world were compared with the IPK in 1889, 1948, and 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK.

The International Prototype Kilogram was commissioned by the General Conference on Weights and Measures (CGPM) under the authority of the Metre Convention (1875), and in the custody of the International Bureau of Weights and Measures (BIPM) who hold it on behalf of the CGPM. After the International Prototype Kilogram had been found to vary in mass over time relative to its reproductions, the International Committee for Weights and Measures (CIPM) recommended in 2005 that the kilogram be redefined in terms of a fundamental constant of nature. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, h. The decision was originally deferred until 2014; in 2014 it was deferred again until the next meeting.[6] CIPM has proposed[7] revised definitions of the SI base units, for consideration at the 26th CGPM. The formal vote, scheduled for 16 November 2018,[8] is expected to be approved[9] and the new definitions will come into force on 20 May 2019.[10]

Other Languages
Afrikaans: Kilogram
Alemannisch: Kilogramm
Аҧсшәа: Акилограмм
العربية: كيلوغرام
aragonés: Kilogramo
asturianu: Quilogramu
Avañe'ẽ: Kilogarámo
Aymar aru: Kilu
azərbaycanca: Kiloqram
Bân-lâm-gú: Kong-kin
башҡортса: Килограмм
беларуская: Кілаграм
беларуская (тарашкевіца)‎: Кіляграм
भोजपुरी: किलोग्राम
български: Килограм
བོད་ཡིག: སྟོང་ཁེའུ།
bosanski: Kilogram
brezhoneg: Kilogramm
català: Quilogram
Чӑвашла: Килограмм
čeština: Kilogram
Cymraeg: Cilogram
dansk: Kilogram
Deutsch: Kilogramm
eesti: Kilogramm
Ελληνικά: Χιλιόγραμμο
español: Kilogramo
Esperanto: Kilogramo
euskara: Kilogramo
فارسی: کیلوگرم
français: Kilogramme
Frysk: Kilogram
furlan: Chilogram
Gaeilge: Cileagram
galego: Quilogramo
贛語: 公斤
客家語/Hak-kâ-ngî: Kûng-kîn
한국어: 킬로그램
հայերեն: Կիլոգրամ
हिन्दी: किलोग्राम
hrvatski: Kilogram
Bahasa Indonesia: Kilogram
interlingua: Kilogramma
íslenska: Kílógramm
italiano: Chilogrammo
עברית: קילוגרם
Basa Jawa: Kilogram
къарачай-малкъар: Килограмм
ქართული: კილოგრამი
қазақша: Килограмм
Kiswahili: Kilogramu
Kreyòl ayisyen: Kilogram
kurdî: Kîlogram
Кыргызча: Килограмм
Latina: Chiliogramma
latviešu: Kilograms
Lëtzebuergesch: Kilogramm
lietuvių: Kilogramas
Limburgs: Kilogram
lingála: Kilogálame
lumbaart: Chilogram
magyar: Kilogramm
македонски: Килограм
മലയാളം: കിലോഗ്രാം
Malti: Kilogramm
Bahasa Melayu: Kilogram
Mìng-dĕ̤ng-ngṳ̄: Gŭng-gṳ̆ng
монгол: Килограмм
မြန်မာဘာသာ: ကီလိုဂရမ်
Nederlands: Kilogram
नेपाली: किलोग्राम
नेपाल भाषा: किलोग्राम
日本語: キログラム
Nordfriisk: Kilogram
norsk: Kilogram
norsk nynorsk: Kilogram
occitan: Quilograma
oʻzbekcha/ўзбекча: Kilogramm
ਪੰਜਾਬੀ: ਕਿਲੋਗ੍ਰਾਮ
پنجابی: کلوگرام
Patois: Kilogram
Plattdüütsch: Kilogramm
polski: Kilogram
português: Quilograma
română: Kilogram
Runa Simi: Kilugramu
русиньскый: Килограм
русский: Килограмм
Gagana Samoa: Kilokalama
संस्कृतम्: किलोग्राम्
Scots: Kilogramme
shqip: Kilogrami
sicilianu: Chilugrammu
Simple English: Kilogram
slovenčina: Kilogram
slovenščina: Kilogram
ślůnski: Kilogram
Soomaaliga: Kiilogaraam
کوردی: کیلۆگرام
српски / srpski: Килограм
srpskohrvatski / српскохрватски: Kilogram
Basa Sunda: Kilogram
suomi: Kilogramma
svenska: Kilogram
Tagalog: Kilogramo
తెలుగు: కిలోగ్రాము
Türkçe: Kilogram
українська: Кілограм
اردو: کلوگرام
vèneto: Chiłogramo
Tiếng Việt: Kilôgam
文言: 公斤
Winaray: Kilogramo
吴语: 公斤
ייִדיש: קילאגראם
粵語: 千克
žemaitėška: Kėluograms
中文: 千克