# 12-hour and 24-hour clock

Time is measured using either the $$12$$-hour clock or the $$24$$-hour clock.

## 12-hour clock

The $$12$$-hour clock notation uses am and pm to indicate morning and afternoon.

• $${am}$$ is the time from $$12$$ midnight and before $$12$$ noon ($$12.00pm$$ is midday)
• $${pm}$$ is the time from $$12$$ midday and before $$12$$ midnight ($$12.00am$$ is midnight)

### For example

• $6.23am$
• $7.45pm$

## 24-hour clock

The $$24$$-hour clock does not require the use of am or pm. Afternoon is indicated by a number bigger than $$12$$.

When converting from the 12-hour clock to the 24-hour clock remember: for any time after 12.59pm, add 12 to the hours.

### For example

• $$6.23pm$$ becomes $$(6.23 + 12) = \text{18:23}$$
• $$7.45pm$$ becomes $$(7.45 + 12) = \text{19:45}$$

The $$24$$-hour clock always uses $$4$$ digits, so for any time before $$\text{10:00}$$ a zero is placed at the beginning.

### For example

• $$\text{01:00}$$ means $$1.00am$$
• $$\text{13:00}$$ means $$1.00pm$$
• $$\text{04:00}$$ means $$4.00am$$
• $$\text{16:00}$$ means $$4.00pm$$
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