PX to Percent Converter

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

Divide the pixel value by the parent font size and multiply by 100: 24px ÷ 16px × 100 = 150%. 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: Is a percentage font size the same as em?

For font-size, yes — both are measured against the parent element, and 1em is exactly 100%. The difference shows up on other properties: percentages on width, padding and margin resolve against the containing block, not the font size, while em always resolves against the font size. So they are interchangeable for type and very different for layout.

Q: Why do people set html { font-size: 100% } instead of 16px?

Because 100% keeps whatever the reader has chosen. If someone has set their browser default to 20px for readability, 100% honours it and the whole page scales; a hard-coded 16px throws that preference away. It is the single easiest accessibility win in a stylesheet.

Convert a pixel font size into the percentage equivalent for any parent size, with the full percentage scale.

Value to convert (px)

Result (%)

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

Percentages are the oldest way to size text relatively in CSS, and they behave exactly like em: 100% is the parent element's font size. This tool takes a pixel value from a design and gives you the percentage that reproduces it, for whatever parent size you are working against. Percentages are still the safest unit for the root element itself — html { font-size: 100% } respects whatever default the reader has chosen, which a pixel value would silently override.

When to Use It

You are converting a design handed over in pixels (px) into a stylesheet that uses percent (%) for accessibility.
You inherited a codebase that mixes units and you need the % equivalent of an existing px value.
You want to check what a px 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

24

At a 16px parent, 24px is 150% — the usual step for a section heading.

16

16px is exactly 100% at the browser default. This is the value to keep on the root element.

12

12px is 75% of a 16px parent. Small print, and about as low as body text should ever go.

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 pixels (px) 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 percent (%) 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 px 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 pixels (px) to percent (%)?

What root font size should I use?

Should I use px or a relative unit?

Is my data sent anywhere?

Is a percentage font size the same as em?

Why do people set html { font-size: 100% } instead of 16px?

Related Tools

Percent to PX Converter

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