Percent to PX Converter

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

Multiply the parent font size by the percentage: 16px × 150% = 24px. 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: Do nested percentages multiply?

Yes, and this is the classic bug. A 150% heading inside a 150% container is 2.25 times the base size, not 1.5. Each percentage resolves against its own parent, so they compound down the tree exactly the way em does. If you want a size that ignores nesting, use rem.

Q: Does a percentage mean the same thing on width as on font-size?

No. On font-size a percentage is relative to the parent element's font size; on width, padding or margin it is relative to the containing block's width. The same 50% can therefore mean two completely different things in the same rule block.

Work out what a percentage font size actually resolves to in pixels, for any parent font size.

Value to convert (%)

Result (px)

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

%	px

What It Does

A percentage in a stylesheet tells you nothing on its own — 150% is 24px inside a normal paragraph and 18px inside a 12px sidebar. This tool resolves the percentage for whatever parent size you enter, so you can check what a rule will actually render. It is most useful when auditing inherited CSS, where percentages have often been nested inside each other and the compounding is no longer obvious from reading the file.

When to Use It

You are converting a design handed over in percent (%) into a stylesheet that uses pixels (px) for accessibility.
You inherited a codebase that mixes units and you need the px 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% of a 16px parent is 24px.

62.5

62.5% of 16px is 10px — the trick used on the root element to make 1rem equal 10px.

87.5

87.5% is 14px, the most common "slightly smaller than body" size.

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 pixels (px) result, or copy the whole conversion table for the sizes you use.

Common Mistakes

Assuming the conversion is fixed. 100% equals the parent element's font size, not a fixed number of pixels — 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 pixels (px)?

What root font size should I use?

Should I use px or a relative unit?

Is my data sent anywhere?

Do nested percentages multiply?

Does a percentage mean the same thing on width as on font-size?

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