2nd/10_Wiki/Topic_CSS/CSS_Grid_12Column.md

---
id: css-grid-12-column-layout
title: "CSS Grid 12-column Layout"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["12-column grid", "repeat(12, 1fr)", "responsive grid layout", "mobile first grid", "named grid lines", "col-start grid", "12 column responsive"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.88
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "grid", "responsive"]
raw_sources: ["https://www.w3schools.com/css/css_grid_12column.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Grid 12-column Layout]]

## 🎯 한 줄 통찰 (One-line insight)
A 12-column grid divides horizontal space into 12 equal fluid `1fr` columns via `grid-template-columns: repeat(12, [col-start] 1fr)`, and because 12 is highly divisible, items can be placed and resized with `grid-column` spans and progressively rearranged through mobile-first media queries. [S1]

## 🧠 핵심 개념 (Core concepts)
- **12-column grid** — a common and flexible method for structuring web page content, particularly for responsive web design. [S1]
- **Equal-width division** — the system divides the available horizontal space into 12 equal-width columns, allowing precise placement and sizing of elements. [S1]
- **Flexibility** — 12 is highly divisible, so designers can create halves, thirds, and quarters (2 columns of 6, 3 columns of 4, 4 columns of 3). [S1]
- **Responsiveness** — a 12-column grid is ideal for building responsive websites that adapt to different screen sizes (desktop, tablet, or mobile) with media queries. [S1]
- **Efficiency** — having a pre-defined structure speeds up the design process. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **`repeat(12, [col-start] 1fr)`** — `repeat(12,..)` repeats the track definition 12 times; `[col-start]` creates a named grid line useful for placing items at specific start points; `1fr` is a fractional unit giving each column an equal, fluid width. [S1]
- **Item placement options** — place/size items with `grid-column: span <number>;`, `grid-column: <start-line> / span <number>;`, or `grid-column: <start-line> / <end-line>;`. [S1]
- **Mobile-first media queries** — design for mobile first, showing sections in source order for small screens, then enhance at 576px and 768px breakpoints. [S1]

## 📖 세부 내용 (Details)
A 12-column grid is a common and flexible method for structuring web page content, particularly for responsive web design. The 12-column grid system divides the available horizontal space into 12 equal-width columns, allowing for precise placement and sizing of elements within the layout. [S1]

**Benefits** [S1]
- **Flexibility:** the number 12 is highly divisible. Designers can easily create designs with halves, thirds, and quarters (2 columns of 6, 3 columns of 4, 4 columns of 3).
- **Responsiveness:** a 12-column grid is ideal for building responsive websites that adapt to different screen sizes (desktop, tablet, or mobile) with media queries.
- **Efficiency:** having a pre-defined structure speeds up the design process.

**Implementation** [S1]
- **Define grid container:** apply `display: grid;` to the container element.
- **Create 12 columns:** use `grid-template-columns: repeat(12, [col-start] 1fr);`, where `repeat(12,..)` tells the grid to repeat the following track definition 12 times (resulting in 12 columns), `[col-start]` creates a named grid line (useful for placing grid items at specific start points), and `1fr` is a fractional unit that represents one fraction of the total available space (so each of the 12 columns will be an equal, fluid width).
- **Place grid items:** grid items can then be placed and sized across these 12 columns using `grid-column`, via `grid-column: span <number>;`, `grid-column: <start-line> / span <number>;`, or `grid-column: <start-line> / <end-line>;`.
- **Media queries:** always design for mobile first. Display the sections in the source order (from top to bottom) for screens less than 576 pixels wide, then enhance at 576px and 768px breakpoints. [S1]

**Complete example** [S1]
```css
* {
  box-sizing: border-box;
}

.container {
  display: grid;
  grid-template-columns: repeat(12, [col-start] 1fr);
  gap: 20px;
}

nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

/* Mobile first */
.container > * {
  border: 1px solid green;
  background-color: beige;
  padding: 10px;
  grid-column: col-start / span 12;
}

@media (min-width: 576px) {
  .sidebar {
    grid-column: col-start / span 3;
    grid-row: 3;
  }
  .ads {
    grid-column: col-start / span 3;
  }
  .content, .footer {
    grid-column: col-start 4 / span 9;
  }
  nav ul {
    display: flex;
    justify-content: space-between;
  }
}

@media (min-width: 768px) {
  .nav {
    grid-column: col-start / span 2;
    grid-row: 2 / 4;
  }
  .content {
    grid-column: col-start 3 / span 8;
    grid-row: 2 / 4;
  }
  .sidebar {
    grid-column: col-start 11 / span 2;
  }
  .ads {
    grid-column: col-start 11 / span 2;
  }
  .footer {
    grid-column: col-start / span 12;
  }
  nav ul {
    flex-direction: column;
  }
}
```

## 🛠️ 적용 사례 (Applied in summary)
The page's applied case is a complete responsive page layout: a 12-column container with `gap: 20px`, full-width stacking on mobile, a 3/9 split at 576px, and a nav/content/sidebar/ads/footer arrangement at 768px. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Define a 12-column fluid grid (language: CSS):
```css
.container {
  display: grid;
  grid-template-columns: repeat(12, [col-start] 1fr);
  gap: 20px;
}
```
Mobile-first full-width default, then span at a breakpoint:
```css
.container > * {
  grid-column: col-start / span 12;
}

@media (min-width: 576px) {
  .content, .footer {
    grid-column: col-start 4 / span 9;
  }
}
```

## ⚖️ 모순 및 업데이트 (Contradictions & updates)
No contradictions found in the source.

## ✅ 검증 상태 및 신뢰도
- **상태:** draft
- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
- **신뢰 점수:** 0.88
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Grid Items]], [[CSS Grid Item Named]], [[CSS RWD Intro]]
- **참조 맥락:** A concrete responsive layout method built on CSS Grid and media queries.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Grid 12-column Layout — https://www.w3schools.com/css/css_grid_12column.asp

## 📝 변경 이력 (Change history)
- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Grid 12-column Layout" page (Astra wiki-curation, P-Reinforce v3.1 format).