40em to px
40em = 640px
At the browser default font size of 16 px. Change it and this number changes — see below.
How it is calculated
One em is 16px, so:
40em × 16 = 640pxReversing it, 640px × 0.0625 returns 40em.
40em at other font sizes
em is measured against the element's own font size, inherited from its parent unless it sets one, so the answer above holds only while that is 16 px. Nested elements each compound on their parent, so this is the value for one level, not for the whole tree.
| Font size | 40em equals |
|---|---|
| 14 px | 560px |
| 16 px (default) | 640px |
| 18 px | 720px |
| 20 px | 800px |
| 24 px | 960px |
Nearby values
| em | px |
|---|---|
| 20em | 320px |
| 24em | 384px |
| 28em | 448px |
| 32em | 512px |
| 36em | 576px |
| 40em | 640px |
| 48em | 768px |
| 56em | 896px |
Frequently asked questions
What is 40em in px?
640px at the default 16 px font size.
How is 40em converted to px?
Multiply by 16: 40 × 16 = 640. To go back, multiply 640 by 0.0625.
Is 640px always the answer?
No. em is relative to the element's own font size, inherited from its parent unless it sets one, so 40em is 640px only while that is 16 px. The table above gives the value at the sizes you are most likely to meet.