What this tool helps you organize
Calculate equal column width after margins and gutters. It is one defined worksheet, not a complete assessment of your circumstances.
Fractional columns need a layout system that handles rounding; this does not create CSS for you.
Method and calculation rules
Column width = (container − two margins − (columns − 1) × gutter) ÷ columns.
Display values are rounded for readability. The calculation uses the entered numbers before display rounding. Whole-unit outputs use the rounding rule stated in the method.
Know your inputs
- Container width (px) — Accepted range: 1 to 100000.
- Margin on each side (px) — Accepted range: 0 to 1000000.
- Columns — Accepted range: 1 to 1000 in whole numbers.
- Gutter width (px) — Accepted range: 0 to 1000000.
A worked example
Illustrative inputs: Container width (px): 1200; Margin on each side (px): 32; Columns: 12; Gutter width (px): 24.
Equal column width: 72.67 px
Inner content width: 1,136 px
Total gutters: 264 px
These sample figures illustrate the formula, not a recommended target or a prediction.
How to use the working copy
Define a single scenario, check the units and replace each sample value that does not match it. Calculate and read all three result components, not just the most favorable number.
Change one assumption to compare scenarios. An edited field makes the previous answer stale; recalculate before downloading or printing. Reset sample clears the open result and restores the example entries.
What the answer cannot establish
Fractional columns need a layout system that handles rounding; this does not create CSS for you.
The tool does not verify the accuracy, completeness or current validity of your inputs. Use authoritative current information and qualified judgement when the decision requires them.
Questions about this worksheet
Are the starting values a suggested target?
No. They show how the arithmetic behaves. Use your own checked values and do not infer a recommendation.
Why is my previous result marked stale?
Changing an input means the displayed answer no longer describes the current fields. Recalculate to refresh it.
Can I share an export?
Review the entries and limitations first. A downloaded file is a working copy, not an independently verified report.
Your entries and privacy
The bundled calculation runs in this open browser page. Inputs are not automatically saved as a server-side calculation history. Browser refresh or navigation may clear them.
Contact messages and technical website records are separate from calculator arithmetic. Read the Privacy Policy for the distinction; do not enter confidential records or credentials.