PX to EM Converter

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

Divide the pixel value by the parent element's font size: 24px ÷ 16px = 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: Why did my em value render at the wrong size?

Almost always nesting. em is measured against the parent element, so an element set to 1.5em inside a container that is itself 1.5em renders at 2.25 times the base size, not 1.5. Check the computed font size of the parent in dev tools and enter that as the base here — or switch the value to rem, which ignores ancestors entirely.

Convert pixels to em units for any parent font size, with a full conversion table and rounding warnings.

Value to convert (px)

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

px	em

What It Does

This tool converts pixels (px) to em in CSS. The conversion is not a fixed ratio — an em is relative to the font size of the *parent* element — so the tool asks for the size that em is measured against and shows the result for that context. It also prints a full conversion table for the common root sizes, so you can read off the values you need without converting one by one, and tells you when the result lands on a fractional pixel that a browser will round.

When to Use It

You are converting a design handed over in pixels (px) into a stylesheet that uses em for accessibility.
You inherited a codebase that mixes units and you need the em 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 the default 16px parent size, 24px is 1.5em — the most common heading step.

1

1px is 0.0625em at a 16px parent. Hairline borders are the usual case where px is the better unit.

18

18px is 1.125em at 16px, but 1.5em if the parent is 12px — this is why em compounds when you nest elements.

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 em result, or copy the whole conversion table for the sizes you use.

Common Mistakes

Assuming the conversion is fixed. 1em 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 em?

What root font size should I use?

Should I use px or a relative unit?

Is my data sent anywhere?

Why did my em value render at the wrong size?

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