Active breakpoints for a viewport width

Front-end developers and designers can enter a width when they need to know which layout thresholds apply to the screen being considered.

See which layout breakpoints apply at a given width, then identify the thresholds that are actually active for that viewport.

How to use

Enter the width in pixels you want to test in the first field.
Add one or more threshold values, one per line, in the second field.
Run the test to see which thresholds match the width you provided.
Read the result, then clear the fields to test another width.
Repeat with other widths if you need to check several screen sizes.

Example

With the sample input, the tool compares the entered width against the listed thresholds and shows which ones are active. The result helps you understand which layout breakpoints apply for that screen width.

Input

Limits and formats

The tool compares numbers; it does not measure a real device or simulate a browser.
Each threshold must be entered on its own line and must remain a numeric value.
A misspelled threshold or a blank line can distort the interpretation.
The result depends only on the values you provide, not on your actual stylesheet.
The tool does not render the page and is not a substitute for device testing.

Where processing happens

The comparison runs inside your browser. The width and thresholds you type are not sent to any service, and nothing is retained after you close the page.

Frequently asked questions

What does an active threshold mean for a width?

A threshold is active when it matches the tested width according to the tool's comparison logic. The result helps you identify which breakpoints are relevant for that screen size.

Can I test several widths at the same time?

No, the tool handles one width per run. Clear the field and run the test again to check another size.

Do the thresholds need to be sorted in a particular order?

You may enter them in any order as long as there is one value per line. The tool compares them with the given width and shows which ones correspond.