Question 1

Why use REM instead of PX?

Accepted Answer

There are two main reasons. 1. Accessibility: Users can change their browser's default font size for better readability. If you use PX, your design stays fixed. If you use REM, your layout scales proportionally, respecting the user's needs. 2. Responsive Design: REM units allow you to easily scale your entire layout (fonts, padding, margins) across different screen sizes just by changing the root font-size within a media query.

Question 2

What is the base font size?

Accepted Answer

The base font size is the font-size of the root element (). By default, this is 16px in most web browsers. Our calculator uses 16px as the default base, but you can change it to match your project's configuration.

Question 3

What is the "62.5%" Trick?

Accepted Answer

Many developers set their CSS html { font-size: 62.5%; }. This sets the base size to 10px (62.5% of 16px). This makes math easier because 1.6rem = 16px and 2.4rem = 24px. You can simulate this in our tool by setting the "Base Font Size" to 10.

Question 4

What is the difference between EM and REM?

Accepted Answer

REM (Root EM) is relative to the root <html> element. EM is relative to the parent element. REM is generally preferred for consistency to avoid 'compounding' size issues.

Pixels (px)	REM	Usage (Approx)
12px	0.75 rem	Small Text / Captions
14px	0.875 rem	Secondary Text
16px	1 rem	Standard Body Text
18px	1.125 rem	Large Body Text
20px	1.25 rem	Sub-headers (H5)
24px	1.5 rem	Medium Headers (H4)
32px	2 rem	Large Headers (H3)
48px	3 rem	Hero Titles (H1)
64px	4 rem	Display Text

PX to REM Converter (CSS Unit Calculator)

How to Calculate REM from Pixels

PX to REM Conversion Table (Base 16px)

Frequently Asked Questions

Dev Tip