How to Use the CSS Units Converter:
Enter a CSS value with its unit (e.g., 16px, 1.5em, 2rem) in the input field. Select the base font size (default 16px) and viewport dimensions if converting viewport units. Choose your target unit and click Convert. The tool will instantly display the converted value in all supported units.
Responsive Design
Convert between px, em, rem, and viewport units when building responsive WordPress themes and layouts.
Theme Development
Convert CSS units to maintain consistent sizing across different screen sizes and devices in WordPress themes.
CSS Calculations
Quickly convert between units when calculating font sizes, spacing, and dimensions in CSS stylesheets.
How Do CSS Units Work?
CSS units can be absolute (px) or relative (em, rem, %, vw, vh). Relative units depend on parent elements, root font size, or viewport dimensions. The converter calculates conversions based on these relationships.
Absolute Units (px)
Pixels are fixed-size units that don't change based on other elements. One pixel equals one device pixel on the screen.
Relative Units (em, rem)
em is relative to the parent element's font size, while rem is relative to the root (html) element's font size. Both scale proportionally.
Viewport Units (vw, vh)
Viewport width (vw) and height (vh) units are relative to the browser viewport size. 1vw = 1% of viewport width, 1vh = 1% of viewport height.
Percentage Units (%)
Percentage units are relative to the parent element's size for the same property, making them useful for responsive layouts.
Using CSS Units in Development:
/* Base font size: 16px */
html { font-size: 16px; }
/* 1.5em = 24px (relative to parent) */
.parent { font-size: 1.5em; }
/* 2rem = 32px (relative to root) */
.child { font-size: 2rem; }Parent: 24px, Child: 32px Understanding em vs rem for responsive typography
Frequently asked questions
em is relative to the parent element’s font size, while rem is relative to the root (html) element’s font size. rem is generally preferred for predictable sizing.
vw (viewport width) and vh (viewport height) are relative to the browser window size. 1vw = 1% of viewport width, useful for responsive designs.
The default base font size is 16px, which is the browser default. You can adjust this in the converter to match your theme’s root font size.
Collect Better Feedback with Userback
This CSS units converter helps you calculate responsive dimensions efficiently, but gathering feedback about layout issues and responsive design problems requires comprehensive visual context. Userback captures detailed visual feedback when users report responsive design issues, layout problems, or font sizing inconsistencies. With automatic screenshot capture, browser information, viewport dimensions, and device details, you get complete visibility into CSS-related issues. When developers need to report unit conversion errors or suggest improvements to responsive design workflows, Userback enables them to submit detailed feedback that includes visual examples, CSS values, and all technical context in a single shareable report.