---
id: css-border-width
title: "CSS Border Width"
category: "Frontend"
status: "draft"
verification_status: "conceptual"
canonical_id: ""
aliases: ["border-width", "CSS border width", "border thickness", "thin medium thick border", "border size"]
duplicate_of: ""
source_trust_level: "B"
confidence_score: 0.9
created_at: 2026-06-23
updated_at: 2026-06-23
review_reason: ""
merge_history: []
tags: ["css", "web", "frontend", "w3schools", "border", "border-width"]
raw_sources: ["https://www.w3schools.com/css/css_border_width.asp"]
applied_in: []
github_commit: ""
---

# [[CSS Border Width]]

## 🎯 한 줄 통찰 (One-line insight)
The `border-width` property sets the thickness of a border, accepting either a specific size (px, pt, cm, em) or one of three predefined keywords — `thin`, `medium`, or `thick` — and like other border properties it takes one to four values for the individual sides. [S1]

## 🧠 핵심 개념 (Core concepts)
- **`border-width`** specifies the width of the four borders. [S1]
- **Specific size** — the width can be set as a specific size in px, pt, cm, em, etc. [S1]
- **Keyword values** — alternatively, three predefined values are allowed: `thin`, `medium`, or `thick`. [S1]
- **Per-side values** — the property can take from one to four values (for the top border, right border, bottom border, and the left border). [S1]
- **Requires border-style** — width is only visible when a `border-style` is also set. [S1]

## 🧩 추출된 패턴 (Extracted patterns)
- **Size or keyword** — choose either an explicit length unit or a relative keyword (`thin`/`medium`/`thick`) per border. [S1]
- **One-to-four value box model** — a single declaration can give every side a different width (e.g. `25px 10px 4px 35px`). [S1]

## 📖 세부 내용 (Details)
**Border Width** [S1]
The `border-width` property specifies the width of the four borders.

The width can be set as a specific size (in px, pt, cm, em, etc.) or by using one of the three pre-defined values: `thin`, `medium`, or `thick`. [S1]

**Example** — mixing specific sizes and keyword values across paragraph classes: [S1]
```css
p.one {
  border-style: solid;
  border-width: 5px;
}

p.two {
  border-style: solid;
  border-width: medium;
}

p.three {
  border-style: dotted;
  border-width: 2px;
}

p.four {
  border-style: dotted;
  border-width: thick;
}
```

**Specific Side Widths** [S1]
The `border-width` property can have from one to four values (for the top border, right border, bottom border, and the left border).

**Example** — supplying multiple values for individual sides: [S1]
```css
p.one {
  border-style: solid;
  border-width: 5px 20px; /* 5px top and bottom, 20px on the sides */
}

p.two {
  border-style: solid;
  border-width: 20px 5px; /* 20px top and bottom, 5px on the sides */
}

p.three {
  border-style: solid;
  border-width: 25px 10px 4px 35px; /* 25px top, 10px right, 4px bottom and 35px left */
}
```

## 🛠️ 적용 사례 (Applied in summary)
The page's own applied examples are the paragraph-class stylesheets above: one demonstrating size vs. keyword widths and one demonstrating two-value and four-value per-side widths. No external project/commit applications found in the source.

## 💻 코드 패턴 (Code patterns)
Single width for all sides (language: CSS):
```css
p.one {
  border-style: solid;
  border-width: 5px;
}
```
Per-side widths, four values (top, right, bottom, left):
```css
p.three {
  border-style: solid;
  border-width: 25px 10px 4px 35px; /* 25px top, 10px right, 4px bottom and 35px left */
}
```

## ⚖️ 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:** 0.90
- **중복 검사 결과:** 신규 생성 (New discovery)

## 🔗 지식 그래프 (Knowledge Graph)
- **상위/루트:** [[CSS Tutorial]]
- **관련 개념:** [[CSS Border Style]], [[CSS Border Color]], [[CSS Border Sides]], [[CSS Border Shorthand]]
- **참조 맥락:** Used together with `border-style` whenever a border's thickness needs to be controlled.

## 📚 출처 (Sources)
- [S1] W3Schools — CSS Border Width — https://www.w3schools.com/css/css_border_width.asp

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