Web Development
PX to REM Converter
Convert pixels to rem units for a given root font size, with a conversion table.
rem = pixels ÷ root font size
Also called pixel to rem · px rem converter
Tech & Media · 11 calculators
Web Development Calculators
px to rem and em conversions, viewport units, aspect ratios, CSS clamp(), grid columns, breakpoints and download time.
Web Development
REM to PX Converter
Convert rem units back to pixels for any root font size.
pixels = rem × root font size
Also called rem to pixel · rem px converter
Web Development
PX to EM Converter
Convert pixels to em units relative to the parent font size, with nesting compounding shown.
em = pixels ÷ parent font size
Also called pixel to em · px em converter
Web Development
EM to PX Converter
Convert em units to pixels relative to the parent element’s font size.
pixels = em × parent font size
Also called em to pixel · em px converter
Web Development
Viewport Units Calculator
Convert between pixels and vw, vh, vmin and vmax for a given viewport size.
1vw = viewport width ÷ 100
Also called vw to px · vh calculator
Web Development
Aspect Ratio Calculator
Find the aspect ratio of any width × height, or calculate a missing dimension for 16:9, 4:3, 21:9 and custom ratios.
W : H = (W ÷ GCD) : (H ÷ GCD)
Also called aspect ratio · 16:9 calculator
Web Development
CSS Clamp Calculator
Build a fluid clamp() value that scales smoothly between two viewport widths.
preferred = intercept + slope × viewport,…
Also called fluid typography calculator · clamp css generator
Web Development
CSS Grid Calculator
Work out grid column widths, gutters and the CSS for a layout of any column count.
column = (container − padding − gaps) ÷ c…
Also called grid layout calculator · column width calculator
Web Development
Responsive Breakpoint Calculator
Media query breakpoints in px, em and rem, with the devices each range covers.
em breakpoint = pixel breakpoint ÷ root f…
Also called media query calculator · breakpoint converter
Web Development
Byte Converter
Convert between 11 digital storage units including bits, bytes, kilobytes, megabytes and more. Accurate factors, instant results.
Also called digital storage unit converter · digital storage conversion
Web Development
Download Time Calculator
How long a file takes to download at a given connection speed, allowing for real-world overhead.
time = file size ÷ (speed × (1 − overhead…
Also called file download time · how long to download
Key web development formulas
| PX to REM Converter | rem = pixels ÷ root font size |
|---|---|
| REM to PX Converter | pixels = rem × root font size |
| PX to EM Converter | em = pixels ÷ parent font size |
| EM to PX Converter | pixels = em × parent font size |
| Viewport Units | 1vw = viewport width ÷ 100 · 1vh = viewport height ÷ 100 |
| Aspect Ratio | W : H = (W ÷ GCD) : (H ÷ GCD) · H = W × b ÷ a |
| CSS Clamp | preferred = intercept + slope × viewport, clamped between the minimum and maximum |
| CSS Grid | column = (container − padding − gaps) ÷ columns |
| Responsive Breakpoint | em breakpoint = pixel breakpoint ÷ root font size |
| Download Time | time = file size ÷ (speed × (1 − overhead)) |
Web Development questions
What is the default root font size?
16px in every major browser, unless the user has changed it in their settings — which is exactly why rem is worth using.
What are the common aspect ratios?
16:9 for HD video and most monitors, 4:3 for older TVs and iPads, 21:9 for ultrawide displays, 1:1 for square social posts, 9:16 for vertical video and 3:2 for many camera sensors.
Why does my 1 TB drive show 931 GB?
The drive is 1 trillion bytes (decimal TB) but the operating system reports in binary GiB, which are 7.4% larger.