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Reference.org
12-hour clock
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<p>The 12-hour clock is a time convention in which the 24 hours of the day are divided into two periods: a.m. (from <a href="/facts/Latin/pM3Kge85">Latin</a> <i>ante meridiem</i>, translating to "before midday") and p.m. (from Latin <i>post meridiem</i>, translating to "after midday"). Each period consists of 12 hours numbered: 12 (acting as 0), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11. The 12-hour clock has been developed since the <a href="/facts/Second_millennium_BC/137VWIhJ">second millennium BC</a> and reached its modern form in the 16th century. </p><p>The 12-hour time convention is common in several English-speaking nations and former <a href="/facts/British_Empire/hrsz0j7A">British colonies</a>, as well as a few other countries. In English-speaking countries: "12 p.m." usually indicates noon, while "12 a.m." means midnight, but the reverse convention has also been used (see § Confusion at noon and midnight). "Noon" and "midnight" are unambiguous. </p> Clock system<table><tbody><tr><th>24-hour clock</th><th>12-hour clock</th></tr><tr><td>00:00</td><td>midnight12:00 p.m.12:00 a.m.</td></tr><tr><td>01:00</td><td>1:00 a.m.</td></tr><tr><td>02:00</td><td>2:00 a.m.</td></tr><tr><td>03:00</td><td>3:00 a.m.</td></tr><tr><td>04:00</td><td>4:00 a.m.</td></tr><tr><td>05:00</td><td>5:00 a.m.</td></tr><tr><td>06:00</td><td>6:00 a.m.</td></tr><tr><td>07:00</td><td>7:00 a.m.</td></tr><tr><td>08:00</td><td>8:00 a.m.</td></tr><tr><td>09:00</td><td>9:00 a.m.</td></tr><tr><td>10:00</td><td>10:00 a.m.</td></tr><tr><td>11:00</td><td>11:00 a.m.</td></tr><tr><td>12:00</td><td>noon12:00 a.m.12:00 p.m.</td></tr><tr><td>13:00</td><td>1:00 p.m.</td></tr><tr><td>14:00</td><td>2:00 p.m.</td></tr><tr><td>15:00</td><td>3:00 p.m.</td></tr><tr><td>16:00</td><td>4:00 p.m.</td></tr><tr><td>17:00</td><td>5:00 p.m.</td></tr><tr><td>18:00</td><td>6:00 p.m.</td></tr><tr><td>19:00</td><td>7:00 p.m.</td></tr><tr><td>20:00</td><td>8:00 p.m.</td></tr><tr><td>21:00</td><td>9:00 p.m.</td></tr><tr><td>22:00</td><td>10:00 p.m.</td></tr><tr><td>23:00</td><td>11:00 p.m.</td></tr><tr><td colspan="3"></td></tr></tbody></table>