Percent to EM Converter

Q: How do I convert percent (%) to em?

Divide by 100: 150% ÷ 100 = 1.5em. The tool does this for you and lets you change the reference size, because that reference is what makes the answer different from one project to the next.

Q: What root font size should I use?

Browsers default to 16px, so 16 is the right starting point unless your stylesheet sets a different size on the html element. If your CSS sets `html { font-size: 62.5% }` — a common trick to make 1rem equal 10px — set the root size to 10 here instead.

Q: Should I use px or a relative unit?

Use relative units (rem, em) for anything that should scale with the reader's font-size preference: type, spacing, and container widths. Pixels are fine for things that genuinely should not scale, such as hairline borders and some shadow offsets. The accessibility rule of thumb is that a user who sets a larger default font size in their browser should see your layout grow with it.

Q: Is my data sent anywhere?

No. The conversion is arithmetic done in your browser — nothing is uploaded, and the page works offline once loaded.

Q: Can I swap % for em everywhere in an old stylesheet?

Only on font-size. A percentage on width, padding, margin or top/left resolves against the containing block, and swapping it for em will change the layout. Convert font sizes freely; leave everything else alone unless you have checked what it resolves against.

Q: Should I convert to em or rem?

Usually rem. A percentage compounds through nesting exactly as em does, so a like-for-like swap to em preserves the existing bugs. Converting to rem breaks the compounding chain and makes sizes predictable — but check each value first, because the rendered size will change wherever nesting was already compounding.

Convert a percentage font size to em — a straight divide by 100, with the cases where the two stop matching.

Value to convert (%)

Result (em)

Root / parent font size

Browsers default to 16px. Use 10 if your CSS sets html { font-size: 62.5% }.

About this conversion

The same value at other root sizes

Root size	Result

Common conversions at 16 px

%	em

What It Does

Converting a percentage font size to em is a divide by 100 — the two units measure against the same thing, so the answer never depends on the parent size. This page exists mostly for the direction people actually work in: modernising an old stylesheet full of percentages into em or rem. The tool shows the equivalent, and points out the one place the swap is not safe, which is any property other than font-size.

When to Use It

You are converting a design handed over in percent (%) into a stylesheet that uses em for accessibility.
You inherited a codebase that mixes units and you need the em equivalent of an existing % value.
You want to check what a % value becomes when the user changes their browser's default font size.
You are writing a design-token scale and need the same step expressed in both units.

Worked Examples

150

150% is 1.5em — identical rendering, shorter to write.

62.5

62.5% is 0.625em. On the root element this is the trick that makes 1rem equal 10px.

100

100% is 1em: inherit the parent size exactly. Both are no-ops, which is sometimes exactly what you want to state explicitly.

Features

Instant two-way conversion

Configurable root/parent font size

Full conversion table for common root sizes

Fractional-pixel rounding warning

Copy the value or the whole table

Works offline in your browser

No uploads or tracking

How to Use

1. Enter the percent (%) value you want to convert. 2. Set the root (or parent) font size the value should be measured against — 16px is the browser default. 3. Read the em result, or copy the whole conversion table for the sizes you use.

Common Mistakes

Assuming the conversion is fixed. 100% is exactly 1em, whatever the parent font size happens to be — the same % value converts differently depending on that size.
Confusing em with rem. `em` is relative to the *parent* element's font size and therefore compounds when nested; `rem` is always relative to the root element and does not.
Setting a px font size on the root element. That overrides the user's browser font-size preference, which defeats the accessibility reason for using relative units at all.
Rounding too early. Keep the fraction (1.375rem, not 1.4rem) — the browser resolves sub-pixel values fine and the rounding error compounds across a scale.

Frequently Asked Questions

How do I convert percent (%) to em?

What root font size should I use?

Should I use px or a relative unit?

Is my data sent anywhere?

Can I swap % for em everywhere in an old stylesheet?

Should I convert to em or rem?

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The conversion runs entirely in your browser. Nothing is uploaded and nothing is stored.