Prefix · quantity · thousand
Means "thousand" in the metric system: kilometer, kilogram, kilowatt, kilobyte.
Written by Bryan López, English teacher · Updated
Kilo- comes from the Greek khilioi, which means "thousand". It is the metric system prefix that multiplies any base unit by 1,000: a kilometer is a thousand meters, and a kilogram is a thousand grams. In everyday talk, people often shorten kilogram to just "kilo".
Metric system prefixes go up by tens, and kilo- is the step right before mega-. In computing, a kilobyte is sometimes counted as 1,000 and sometimes as 1,024 bytes, depending on the context. And a useful detail if you travel: in the United States pounds are used more than kilos, so you will see kilo- mostly in science, technology and international labels.
Combines with SI base units to multiply them by 1,000:
Pronunciation: /ˈkɪl.oʊ/. Official abbreviation: k (lowercase). In everyday speech, "a kilo" = 1 kilogram.
kilo-/ˈkɪl.oʊ/
Tap the button to hear how the prefix sounds. Each word in the table has its own audio.
The prefix kilo- never changes: it always means ×1,000. The confusion arises because the US uses the imperial system (miles, pounds, gallons) while most of the world uses the metric system (kilometres, kilograms, litres). Quick conversion: km × 0.6 ≈ miles; miles × 1.6 ≈ km.
A trick to remember it
Think of a kilometer, a thousand meters: kilo- = a thousand. kilometer, kilogram.
Exercise 1 · Form the word
Exercise 2 · Pick the right one
Why do nutritionists say "calorie" when they technically mean "kilocalorie"?
The prefix kilo- means "thousand" in the metric system: kilometer, kilogram, kilowatt, kilobyte.
The prefix kilo- is pronounced /ˈkɪl.oʊ/. For example, "kilometer".
"meter" becomes "kilometer". It is a typical example of the kilo- prefix.
un-, re-, pre-, dis-, over-, in-... every beginning you need to unlock thousands of English words at once.