Billion

A billion is exactly one thousand million, 1,000,000,000, or 109.

U.S. usage  |  Value  |  Former British usage

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thousand  |  103 = 1,000  |  thousand
million  |  106 = 1,000,000  |  million
billion  |  109 = 1,000,000,000  |  thousand million or milliard
trillion  |  1012 = 1,000,000,000,000  |  billion
quadrillion  |  1015 = 1,000,000,000,000,000  |  thousand billion or (very rarely) billiard
quintillion  |  1018 = 1,000,000,000,000,000,000  |  trillion