Visual CSS Size Preview Tool
Enter pixel values to preview box size and get conversions in REM, EM, %, and VW.
Live Preview
Width:
Height:
📐 How to Use the Visual CSS Size Preview Tool (With Live Conversions)
The Visual CSS Size Preview Tool helps web designers and developers preview an element’s actual size and instantly convert pixel values into REM, EM, %, and VW units. This ensures you build responsive layouts without guessing or manual calculations.
🧰 What the Tool Does
Enter a width and height in pixels and get real-time:
- REM and EM conversions (based on base font size)
- Percentage relative to container width
- VW units based on viewport width
- A live preview box reflecting exact pixel dimensions
- Copy-ready CSS snippet with all values in one place
✅ Step-by-Step Guide
1. Set Width and Height (px)
Enter how wide and tall your element should be.
Example: Width: 300px, Height: 150px
2. Enter the Base Font Size
Used to calculate rem and em. Most browsers default to 16px, so keep that unless your site uses something else.
Example: 16px (default)
3. Set Container Width
This defines the full width of the parent layout (for `% calculations).
Example: Container Width: 1200px
4. Set Viewport Width
Used to calculate vw (viewport width unit).
Example: Viewport Width: 1440px (for desktop layouts)
5. Preview the Box
You’ll see a box in the exact pixel size you entered — helpful to visualize before coding.
6. Read the Conversions
For both width and height, you’ll see:
Text
PX: 300px
REM: 18.75rem
EM: 18.75em
%: 25%
VW: 20.83vw
7. Copy the CSS Snippet
Click the 📋 Copy CSS Snippet button. Example output:
CSS
/* Width: 300px | Height: 150px */
width: 300px; /* 18.75rem, 20.83vw, 25% */
height: 150px; /* 9.38rem, 10.42vw, 12.5% */
Paste it into your project and adjust as needed!