PX to REM Converter
Bidirectional px/rem converter with Tailwind CSS matching, fluid clamp() typography generator, and batch CSS conversion.
How to Use
Convert between pixels and rem units instantly. The tool updates both values as you type, so you always see the conversion in real time.
- Set your base font size at the top. The default is 16px, which is the browser standard. If your project uses a different root font size, change it here.
- Enter a value in either the PX or REM input field. The other field updates automatically using the formula:
rem = px / base. - View Tailwind CSS matches below the converter. If your value corresponds to a Tailwind spacing unit or font size class, the matching utility names are shown with copy buttons.
- Generate fluid typography using the "Fluid Type" tab. Enter min/max font sizes and viewport widths to produce a
clamp()function that scales smoothly without media queries. - Batch convert CSS using the "Batch CSS" tab. Paste an entire CSS block and all px values are converted to rem (or vice versa) while preserving 1px borders and syntax structure.
About This Tool
The rem unit (root em) is relative to the root element's font size, typically 16px in browsers. Using rem instead of px makes layouts adapt to user font size preferences and simplifies responsive scaling — changing the root font size proportionally scales every rem-based measurement.
Why REM Over PX?
Pixels are absolute units that ignore user settings. If a user sets their browser's default font size to 20px for readability, text set in px stays the same while text set in rem scales proportionally. The WCAG 2.1 accessibility guidelines recommend relative units for text sizing. Most CSS frameworks (Tailwind, Bootstrap) use rem as their base unit for spacing and typography.
Fluid Typography with clamp()
The clamp(min, preferred, max) CSS function creates fluid scaling between two breakpoints using a single line. The preferred value uses a linear interpolation formula: preferred = intercept(rem) + slope(vw). This eliminates the need for multiple media query breakpoints for font size adjustments. The Fluid Type tab calculates this formula automatically.
Tailwind CSS Integration
Tailwind uses a spacing scale based on 0.25rem (4px) increments: p-4 equals 1rem (16px), p-6 equals 1.5rem (24px). Font sizes use named classes: text-base (1rem), text-xl (1.25rem), text-2xl (1.5rem). The converter shows matching Tailwind utilities for any value that maps to the default scale.
Why Use This Tool
PX-to-REM conversion is a daily workflow for web developers. Here are the most common use cases:
- Design-to-code translation — Designers deliver specs in pixels. Developers need rem values. This tool bridges the gap instantly, and the Tailwind matcher shows the exact utility class to use.
- Accessibility compliance — Using rem for font sizes ensures text scales with user preferences. The WCAG Success Criterion 1.4.4 requires text to be resizable to 200% without loss of content.
- Responsive typography — The Fluid Type generator creates a single CSS line that scales text smoothly between mobile and desktop viewports, eliminating media query breakpoints.
- Legacy code migration — Use the Batch CSS tab to convert entire stylesheets from px to rem in one pass. The tool preserves 1px border values and maintains CSS syntax.
- Quick reference — The reference table provides a cheat sheet of common px-to-rem conversions with Tailwind class mappings, useful during code reviews or pair programming.
Privacy
All conversion and CSS processing happens in your browser. No CSS code is sent to any server. Safe for proprietary design systems and internal stylesheets.