FAQ
PX to REM Conversion FAQ
Answers to the most common questions about converting px to rem, choosing the right CSS unit, and understanding how base font size affects your layouts. Use the px to rem calculator for instant conversions.
How do I convert px to rem?
Divide the pixel value by the root font size. With the standard 16px base, the formula is rem = px / 16. For example, 16px equals 1rem, 24px equals 1.5rem, and 32px equals 2rem. If your project uses a different root font size, divide by that value instead.
How do I convert rem to px?
Multiply the rem value by the root font size. With a 16px base, the formula is px = rem * 16. So 2rem equals 32px, 1.5rem equals 24px, and 0.5rem equals 8px. You can use this calculator as a rem to px converter by entering a rem value or swapping the unit direction.
What is 16px in rem?
16px equals 1rem when the base font size is 16px, which is the browser default. This is the most common reference point for px to rem conversion because most browsers and CSS frameworks start with a 16px root.
What is 1rem in pixels?
1rem equals whatever the root font size is set to. In most browsers, the default root font size is 16px, so 1rem equals 16px. If your CSS sets the html element to a different size, like 14px or 18px, then 1rem equals that value instead.
What is the difference between rem and em?
rem is always relative to the root element's font size, making it consistent across your entire page. em is relative to the font size of the current element or its nearest parent, so it compounds when elements are nested. Most developers use rem for global sizing and em for component-level scaling.
Why does the base font size matter?
The base font size is the root value that every rem calculation depends on. If your project sets the html element to 14px instead of the default 16px, then 1rem equals 14px and all conversions shift. Always match the base font size in this calculator to your project's actual root font size for accurate results.
What is the default font size in browsers?
All major browsers default to a 16px root font size unless the user or a stylesheet changes it. This is why most px to rem conversion tables use 16px as the base. Users can override this in their browser settings for accessibility, which is one reason developers use rem instead of px for font sizes.
Is rem better than px for accessibility?
Yes. When you use rem for font sizes, your text scales if a user increases their browser's default font size for readability. Hard-coded px values ignore that preference entirely. Using rem for typography and spacing helps meet WCAG accessibility guidelines and makes your site more usable for people with low vision.
Can I use this calculator for print units like pt, mm, and cm?
Yes. The converter supports common print and physical units including points (pt), picas (pc), millimeters (mm), centimeters (cm), inches (in), and quarter-millimeters (q). This is helpful when translating designs between screen CSS, PDFs, and print specifications.
How do I set the base font size in CSS?
Set the font-size property on the html element. For example, html { font-size: 18px; } changes the root to 18px, which means 1rem now equals 18px. You can also use a percentage like html { font-size: 62.5%; } to set the root to 10px for easier mental math, though the standard 16px base is more common.
Which CSS unit should I use?
Use rem for font sizes, margins, and padding that should scale with user preferences. Use em for spacing inside components that should scale with the component's own text. Use px for borders, shadows, and details that need exact pixel control. Use percent for fluid widths and inherited text sizing. The right choice depends on whether the value should scale and what it should scale relative to.
How do I convert rem to px in JavaScript?
Multiply the rem value by the computed root font size: parseFloat(getComputedStyle(document.documentElement).fontSize) * remValue. This reads the actual root font size the browser is using, which accounts for user overrides and CSS changes, and gives you the correct pixel equivalent.