# How do I convert a pixel-based column grid into a fluid grid, and what checks catch errors?

- id: art_01M5NNSW5TJYP4CZJKY0WV7QZE
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T17 · tags: none
- updated: 2026-10-24T00:43:35.476Z
- url: https://veyrul.com/articles/art_01M5NNSW5TJYP4CZJKY0WV7QZE

Marcotte (A List Apart, 2009-03-03) gives one formula, target / context = result, applied to a 988 px grid of seven 124 px columns and 20 px gutters: 700/988 = 70.85%, 144/988 = 14.575%, and after the container changes the divisor changes too (700/844 = 82.938%). It also caps width with max-width in ems and warns that browsers round sub-pixel widths. Carbon and GOV.UK document the same idea in current systems: Carbon column widths between breakpoints are a percentage of the grid area, GOV.UK widths are percentages from quarters to full. The article is 2009 practice and predates CSS Grid and media-query-driven systems.

Marcotte (A List Apart, 2009-03-03) gives one formula, target / context = result, applied to a 988 px grid of seven 124 px columns and 20 px gutters: 700/988 = 70.85%, 144/988 = 14.575%, and after the container changes the divisor changes too (700/844 = 82.938%). It also caps width with max-width in ems and warns that browsers round sub-pixel widths. Carbon and GOV.UK document the same idea in current systems: Carbon column widths between breakpoints are a percentage of the grid area, GOV.UK widths are percentages from quarters to full. The article is 2009 practice and predates CSS Grid and media-query-driven systems.

Curator qualifications: Curator recomputed 700/988 = 70.8502%, 144/988 = 14.5749%, 700/844 = 82.9384%, matching Marcotte's 70.85%, 14.575% and 82.938%.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

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      "url": "https://alistapart.com/article/fluidgrids/",
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      "url": "https://github.com/alphagov/govuk-frontend/tree/6c365ebaa998bc2a4ea20fe89c583907e38245dd/packages/govuk-frontend/src/govuk",
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Evidence claims:
- [sourced_fact] Marcotte (A List Apart, 2009-03-03) gives one formula, target / context = result, applied to a 988 px grid of seven 124 px columns and 20 px gutters: 700/988 = 70.85%, 144/988 = 14.575%, and after the container changes the divisor changes too (700/844 = 82.938%). It also caps width with max-width in ems and warns that browsers round sub-pixel widths. Carbon and GOV.UK document the same idea in current systems: Carbon column widths between breakpoints are a percentage of the grid area, GOV.UK widths are percentages from quarters to full. The article is 2009 practice and predates CSS Grid and media-query-driven systems. · locator: candidate evidence excerpts · source: https://alistapart.com/article/fluidgrids/

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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