A pixel and EM unit converter for front-end developers featuring custom base font sizes and real-time two-way conversion.
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Still manually calculating conversions between pixels (px) and relative units (em) in CSS? This tool directly addresses the core conversion needs for responsive layouts in front-end development. The PX to EM Converter is an online calculator based on the formula em = px / base font size. It performs real-time, two-way conversions between pixel and EM values while allowing you to customize the root font size (base value). Its primary focus is on CSS length units, outputting precise conversion results to help you quickly adapt to different screens and design specifications.
<html> style definitions.Q: What is the px to em formula?
A: EM value = Pixel value / Root font size. For example, 24px is equal to 1.5em when the root font size is 16px.
Q: How do I determine the correct root font size for my project?
A: Check the font-size property defined in the <html> element of your CSS. The most common value is 16px, but it may vary depending on your design system or framework (like Bootstrap). Make sure it matches exactly.
Please ensure your input consists of pure numbers; the tool will ignore non-numeric characters. The accuracy of the conversion results depends entirely on whether your "Root Font Size" setting matches your project's actual base value. This tool only handles numerical conversions and does not account for CSS inheritance or units like rem. All calculations are performed locally in your browser, so there is no risk of data upload.
In responsive design, it is highly recommended to prioritize relative units (such as em and rem). The "relative" nature of EM makes it particularly suitable for controlling padding, margins, or element widths that are closely tied to font size, allowing them to scale adaptively. A typical example: if a design mock-up specifies a button's padding as "0.75 times the font size," and the root font is 16px, you can directly input 0.75em to get 12px. If the root font is later changed to 14px, it automatically scales to 10.5px without requiring recalculation.