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Image tools

AI Image UpscalerHEIC to JPG ConverterBatch Watermark ImagesImage ResizerImage CompressorImage CropperImage Format ConverterContent Credentials InspectorAI Image ScannerBackground Remover

Developer & CSS

CSS Corner Shape GeneratorCSS Clamp GeneratorREM/EM/PX MatrixTailwind Spacing ConverterTailwind Grid BuilderAspect Ratio CalculatorColor ConverterViewport Unit ConverterContrast Checker

Unit converters

PX to REM ConverterREM to PX ConverterPX to EM ConverterEM to PX ConverterREM to EM ConverterPounds to Kilograms ConverterKilograms to Pounds ConverterCentimeters to Inches ConverterInches to Centimeters Converter
Browser-based utilities

Free CSS and developer tools

Build responsive interfaces, generate CSS, convert color formats, and check text contrast. These tools run in your browser and explain their formulas and assumptions.

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Tools for CSS, layout, and accessibility

Choose a CSS or layout tool below. For photo enhancement, background removal, compression, and conversion, explore our dedicated image tools.

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CSS designCSS Corner Shape Generator

Generate CSS corner-shape values with clickable demos, live per-corner controls, custom superellipse curves, and copy-ready CSS.

Open tool ↗CSS typographyCSS Clamp Generator

Generate a responsive CSS clamp() value from minimum and maximum font sizes and viewport widths, with pixel and REM output.

Open tool ↗CSS unitsREM/EM/PX Matrix

Convert one CSS length across PX, REM, and EM with adjustable root and element font sizes and a live comparison matrix.

Open tool ↗Tailwind CSSTailwind Spacing Converter

Convert Tailwind spacing numbers to REM and pixels using an adjustable spacing variable and root font size, with utility examples.

Open tool ↗Tailwind CSSTailwind Grid Builder

Build responsive Tailwind CSS grids visually with a custom grid maker. Drag, edit, resize, reorder, and delete blocks across every default breakpoint.

Open tool ↗Responsive layoutAspect Ratio Calculator

Simplify width and height into an aspect ratio, calculate a proportional target height, and copy CSS aspect-ratio code.

Open tool ↗CSS colorColor Converter

Convert HEX, RGB, and HSL colors in either direction, including alpha transparency, with a live preview and copyable CSS output.

Open tool ↗Responsive CSSViewport Unit Converter

Convert pixels to VW, VH, Vmin, and Vmax using an adjustable viewport width and height, with copyable CSS results.

Open tool ↗AccessibilityContrast Checker

Check two HEX colors against WCAG 2.2 AA and AAA text contrast thresholds with a live preview and exact contrast ratio.

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Learn the context

Guides that explain the tradeoffs

Conversion numbers are useful only when the CSS context and intended behavior are understood.

CSS units guideREM vs EM: How CSS Relative Units Actually Differ

Understand the difference between REM and EM, how each resolves in CSS, when values compound, and which unit fits a design-system decision.

Read guide ↗CSS typography guideRoot Font Size and REM: A Practical CSS Guide

Learn how the root font size controls REM values, why 16px is a common assumption rather than a universal constant, and how to test responsibly.

Read guide ↗Design handoff guideHow to Convert Figma PX Values to REM

Move pixel-based Figma measurements into a REM-based CSS system without losing scale, context, accessibility, or design-token intent.

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