What is the default base font size?

The tool defaults to 16px, which is the browser default. You can change this to match your project's root font size for accurate rem calculations.

How does rem differ from em?

rem is relative to the root element's font size (usually 16px). em is relative to the parent element's font size, which can cascade. rem is more predictable for consistent spacing.

Can I convert viewport units?

Yes. Enter your viewport width and height and the tool will convert between vw, vh, vmin, vmax and pixel values accurately.

Convert CSS Units Online Free

Convert between CSS units instantly: px, rem, em, vw, vh, pt, cm and more. Set your base font size and viewport dimensions, then convert any value between units. All calculations run in your browser for instant results.

Open CSS Unit Converter

Conversion Example

Base font size: 16px
Viewport: 1920 x 1080

16px  = 1rem = 1em = 12pt
24px  = 1.5rem = 18pt
32px  = 2rem = 24pt
100vw = 1920px
100vh = 1080px
50vw  = 960px

Common Use Cases

Converting pixel values from design files to rem for responsive CSS
Calculating viewport-relative units for fluid layouts
Translating print units (pt, cm, in) to screen units (px)
Setting consistent spacing scales in rem

Frequently Asked Questions

What is the default base font size?: The tool defaults to 16px, which is the browser default. You can change this to match your project's root font size for accurate rem calculations.
How does rem differ from em?: rem is relative to the root element's font size (usually 16px). em is relative to the parent element's font size, which can cascade. rem is more predictable for consistent spacing.
Can I convert viewport units?: Yes. Enter your viewport width and height and the tool will convert between vw, vh, vmin, vmax and pixel values accurately.