The PX to Percentage Converter turns a pixel value into a percentage of its container width, which is useful for responsive, fluid CSS layouts and grids.
Percentages let an element resize with its container instead of staying a fixed number of pixels, which is the foundation of fluid design. Enter the pixel value and the container width, and the converter gives you the percentage (and converts back), so you can swap a rigid pixel width for one that flexes.
How to convert px to percentage
- Enter the pixel value.
- Enter the container (parent) width in pixels.
- Read the percentage; it also converts percentage back to px.
The px to percentage formula
percentage = (px ÷ container width) × 100. For a 300px element inside a 1200px container, that’s (300 ÷ 1200) × 100 = 25%.
What the percentage is relative to
A percentage is always relative to something, and which dimension depends on the property. width and left/right offsets are relative to the containing block’s width; height is relative to the container’s height (which must be defined, or the height is ignored). A surprising but useful rule: padding and margin percentages — even top and bottom — are calculated from the container’s width, not its height. That quirk is what makes the classic “padding-bottom” trick work for fixed aspect-ratio boxes.
When to use percentage widths
Percentages are ideal for fluid columns and grids that should share the available space, for images set to max-width: 100% so they never overflow their container, and for layouts that must adapt to any screen without fixed breakpoints. For sizing relative to the viewport rather than the parent, use vw and vh instead; for type and spacing that scale from the root, use rem.
Frequently Asked Questions
How do I convert px to percentage?
Divide the pixel value by the container width and multiply by 100. A 300px item in a 1200px container is 25%.
When should I use percentage widths?
Percentages make elements scale with their container, which is ideal for responsive layouts and fluid grids.
What container width should I use?
Use the width of the parent element the value sits inside, since percentages are relative to the parent.