# Online Ruler — llms-full.txt
> Complete reference for the Online Ruler tool: https://ruler.kiveo.org

# Online Ruler
> Pixel-perfect online ruler for your screen
> https://ruler.kiveo.org/en

This free online ruler lets you measure anything on your screen in centimeters, millimeters, inches, or pixels. Calibrate once and your online ruler stays accurate forever.

## Features

- **Smart Auto-Detect**: Automatically identifies your device from a database of 100+ profiles and sets the correct PPI, so the online ruler is accurate from the very first click.
- **3 Calibration Methods**: Choose auto-detect, manual screen diagonal input, or credit card overlay for the best accuracy on any device.
- **Multi-Edge Placement**: Place rulers on any edge of your screen — top, bottom, left, right, or any combination — and the online ruler stays aligned on every edge.
- **Click-to-Measure**: Click any two points on the screen to instantly measure the distance between them. Works horizontally, vertically, and diagonally.
- **Live Cursor Position**: See real-time cursor coordinates as you move across the screen. Perfect for precise alignment and positioning tasks.
- **Dark Mode**: Switch between light and dark themes for comfortable measuring in any lighting. Your system preference is respected automatically.

## How It Works

1. **Calibrate your screen.** Choose auto-detect, screen diagonal, or credit card calibration. It takes a few seconds, and your online ruler keeps that calibration for future visits.
2. **Place your rulers.** Select which edges to display rulers on — top, bottom, left, right, or all four. Pick your unit: cm, mm, inches, or pixels.
3. **Measure anything.** Click two points to measure distances, track your cursor position in real time, or use the edge rulers for a quick reference — the online ruler shows every reading instantly.

## Calibration Methods

Auto-Detect Device (Fastest): We match your screen resolution, pixel ratio, and user agent against our database of 100+ device profiles to find the correct PPI for the online ruler.

Screen Diagonal (Most Common): Enter your monitor diagonal in inches (usually printed on the box or in specs). We calculate the exact PPI from your screen resolution.

Credit Card (Most Accurate): Place any standard credit card on screen and adjust until it matches. Uses the ISO standard card size of 85.6mm × 54mm — the most accurate online ruler calibration.

## FAQ

### How accurate is the online ruler?

After proper calibration, this online ruler achieves near pixel-perfect accuracy — typically within 0.5mm on well-calibrated screens. Accuracy depends on your calibration method: auto-detect works well for known devices, while credit card calibration gives the best results on any screen.

### How do I calibrate the ruler for my screen?

Pick one of three methods: Smart Auto-Detect (recognizes your device from 100+ profiles), Screen Diagonal (enter your display diagonal in inches), or Credit Card calibration (match a standard card outline on screen). Credit card calibration is the most accurate.

### What units can I measure in?

The online ruler supports four units: centimeters (cm), millimeters (mm), inches (in), and pixels (px). Switch between them at any time from the toolbar or with keyboard shortcuts.

### Does it work on mobile devices?

Yes. The ruler works on tablets and phones with touch support. For the best accuracy we recommend a laptop or desktop monitor, since mobile screens are small and harder to calibrate precisely.

### Do I need to install anything?

No installation is required. The online ruler runs entirely in your browser. Visit the page, calibrate once, and start measuring — your calibration is stored locally.

### Can I measure diagonal distances?

Yes. Click two points anywhere on the screen and the tool shows the straight-line distance, plus the horizontal and vertical components, in your selected unit.

### Is the ruler free to use?

Absolutely. The online ruler is completely free, with no ads, no account required, and no usage limits.

### Can I place rulers on different edges?

Yes. Show rulers on the top, bottom, left, or right edge — or any combination. Use the edge selector in the toolbar to choose your layout.

# Keyword Guides

## Ruler in CM — Online Ruler Measured in Centimeters

URL: https://ruler.kiveo.org/en/ruler-in-cm

Need a ruler in cm? This online ruler shows centimeters directly on your screen edge, with millimeter subdivisions for fine measurements. Calibrate once with the credit card method, and every ruler in cm reading stays accurate for good.

### How to use the ruler in cm

Open the tool above and select cm as the unit. The top and left edges of your screen now display a ruler in cm starting from the corner. For a more precise calibration, press Calibrate and pick the credit card method — it takes ten seconds and makes the cm ruler in cm nearly pixel-perfect. You can show the cm ruler on any edge: top, bottom, left, or right.

### Why calibrate before using a ruler in cm

A screen is not a physical object of fixed size, so a ruler in cm is only as good as your PPI calibration. Auto-detect recognizes over 100 devices instantly, the screen diagonal method works for any monitor, and credit card calibration gives the most accurate ruler in cm on unknown displays. After calibration, this online ruler is typically accurate within 0.5mm.

### Centimeter reference chart for your screen

Use this quick reference to check whether your cm ruler in cm reads true: hold a real centimeter ruler against the screen and compare a few marks. If the numbers drift, recalibrate the online ruler and the cm scale will line up again.

Centimeter conversion reference:
Centimeters | Millimeters | Inches
1 cm | 10 mm | 0.394 in
5 cm | 50 mm | 1.969 in
10 cm | 100 mm | 3.937 in
20 cm | 200 mm | 7.874 in
30 cm | 300 mm | 11.811 in

### How accurate is this ruler in cm?

After credit card calibration, the ruler in cm is accurate to about 0.5mm on most screens. Auto-detect and diagonal calibration also produce a reliable ruler in cm, usually within 1mm.

### Can I measure real objects with a ruler in cm?

Yes — place a physical object against a calibrated screen (a credit card is 8.56cm wide) and the cm ruler in cm will read its true size.

### Does the ruler in cm work on phones?

It does. On mobile, calibrate with the credit card method so your ruler in cm stays accurate even on small displays.

## Ruler in Inches — Online Ruler Measured in Inches

URL: https://ruler.kiveo.org/en/ruler-in-inches

This ruler in inches lays an inch scale along the edge of your screen, complete with 1/16-inch marks. It is the same online ruler trusted for measuring screen elements, printed layouts, and any object you place against the display — just switch the unit to inches.

### How to use the ruler in inches

Select in as the unit in the toolbar and the ruler in inches appears on the chosen screen edges, starting at the top-left corner. Whole-inch numbers are labeled, half-inch marks are longer, and the smallest ticks show sixteenths of an inch. Press M to enter measure mode and the ruler in inches can verify the distance between any two points.

### Calibration for an accurate ruler in inches

An uncalibrated screen assumes a default PPI, which makes any ruler in inches drift on non-standard displays. Run Smart Auto-Detect for known devices, enter your monitor diagonal for a quick fix, or use credit card calibration for the most accurate ruler in inches. Your calibration is stored locally and reused on every visit.

### Inches to centimeters quick chart

The ruler in inches doubles as a converter: switch units with the U key and the same measurement is redrawn in centimeters. Use the chart below to sanity-check the ruler in inches against known object sizes.

Inch conversion reference:
Inches | Centimeters | Millimeters
1 in | 2.54 cm | 25.4 mm
3 in | 7.62 cm | 76.2 mm
6 in | 15.24 cm | 152.4 mm
8.56 in (credit card) | 21.74 cm | 217.4 mm
12 in | 30.48 cm | 304.8 mm

### How do I get a true ruler in inches on my screen?

Calibrate first — the credit card method makes this ruler in inches accurate to roughly 0.5mm, because the card is exactly 3.37 inches wide.

### Does the ruler in inches show fractions?

The scale marks every 1/16 inch. The ruler in inches labels whole inches, and the measure readout shows decimals like 4.75 in.

### Can I switch the ruler in inches to centimeters?

Yes, press U or tap the unit buttons — the same online ruler redraws instantly in cm, mm, or pixels.

## Pixel Ruler — Measure Your Screen in Pixels

URL: https://ruler.kiveo.org/en/pixel-ruler

A pixel ruler that never needs a tape measure: click two points and read the exact distance in pixels. This online ruler also shows px positions for your cursor, so UI engineers can verify spacing, icon sizes, and layout gutters without opening a design tool.

### How the pixel ruler works

Choose px as the unit and every tick on the edge rulers switches to pixel steps — major marks every 100px, medium marks every 50px, fine ticks every 10px. Press M to activate the pixel ruler measure mode, click two points, and the readout gives the dx, dy, and diagonal distance in px. The cursor readout always shows live X/Y pixel coordinates.

### Pixel ruler vs calibrated units

The pixel ruler is always exact, because pixels are your screen’s native unit: one CSS pixel is one unit, no calibration required. Switching to cm, mm, or inches uses your saved PPI calibration, so the same online ruler can output both px and real-world units for the same measurement.

### What designers build with a pixel ruler

Common uses: checking that a button is 44px tall, verifying 8px spacing grids, comparing a live build against a mockup, and measuring icon hit areas. Anywhere you would reach for a design inspector, this pixel ruler does the job in one click.

### Does the pixel ruler need calibration?

No. The pixel ruler measures in native screen pixels, so it is accurate by definition. Calibration only affects cm, mm, and inches modes on this online ruler.

### Can the pixel ruler show CSS pixels or device pixels?

It follows your browser’s coordinate system (CSS pixels), which matches what you type into CSS. Device-pixel ratios are handled automatically during calibration.

### Is the pixel ruler free?

Yes — this pixel ruler is completely free, works offline after loading, and stores nothing but your preferences locally.

---

# 在线尺子
> 像素级精准的屏幕测量工具
> https://ruler.kiveo.org/zh

这款免费的在线尺子支持用厘米、毫米、英寸和像素测量屏幕上的任何物体。只需校准一次，在线尺子即可永久保持精准。

## Features

- **智能自动识别**: 从 100+ 设备数据库中自动识别你的设备，并设置正确的 PPI，在线尺子从第一次点击起就是精准的。
- **3 种校准方式**: 可选择自动识别、手动输入屏幕对角线或信用卡贴合校准，在任何设备上都能获得最佳精度。
- **多边缘放置**: 可在屏幕任意边缘放置尺子 — 顶部、底部、左侧、右侧或任意组合，灵活满足各种测量需求。
- **点击测量**: 点击屏幕上任意两点即可立即测量它们之间的距离，支持水平、垂直和对角线方向。
- **实时光标定位**: 移动鼠标时实时显示光标坐标，非常适合需要精确对齐和定位的场景。
- **暗色模式**: 在明暗主题之间切换，任何光线环境下都能舒适测量，并自动跟随系统偏好。

## How It Works

1. **校准你的屏幕。** 选择自动识别、屏幕对角线或信用卡校准方式，只需几秒钟，你的在线尺子会记住该配置供以后访问使用。
2. **放置尺子。** 选择要显示尺子的边缘 — 顶部、底部、左侧、右侧或四条边，并选择单位：厘米、毫米、英寸或像素。
3. **测量任何东西。** 点击两点测量距离，实时跟踪光标位置，或直接用边缘尺子快速参考。在线尺子会立即显示所有读数。

## Calibration Methods

自动识别设备 (最快): 我们将屏幕分辨率、像素密度和用户代理与 100+ 设备数据库进行匹配，为在线尺子找到正确的 PPI。这是最常用的校准方式。

屏幕对角线 (最常用): 输入显示器对角线尺寸（通常印在包装盒或规格表上），我们据此计算屏幕的精确 PPI。

信用卡 (最精准): 将标准信用卡放在屏幕上并调整至吻合，使用 ISO 标准卡片尺寸 85.6mm × 54mm — 这是在线尺子最精准的校准方式。

## FAQ

### 在线尺子有多精准？

正确校准后，这款在线尺子可达到接近像素级的精度 — 校准良好时误差通常在 0.5mm 以内。精度取决于校准方式：自动识别适合已知设备，信用卡校准在任何屏幕上效果最好。

### 如何为我的屏幕校准尺子？

三种方式任选其一：智能自动识别（从 100+ 设备库识别你的设备）、屏幕对角线（输入显示器对角线英寸数）或信用卡校准（在屏幕上匹配标准卡片轮廓）。信用卡校准最精准。

### 可以用哪些单位测量？

在线尺子支持四种单位：厘米（cm）、毫米（mm）、英寸（in）和像素（px）。可随时通过工具栏或键盘快捷键切换。

### 支持移动设备吗？

支持。尺子可在平板和手机上触控使用。为获得最佳精度，建议使用笔记本或台式机显示器，因为手机屏幕较小，校准更难精确。

### 需要安装什么吗？

完全无需安装。在线尺子完全在浏览器中运行，打开页面、校准一次即可开始测量，校准值保存在本地。

### 可以测量对角线距离吗？

可以。点击屏幕上任意两点，工具会显示直线距离，以及水平和垂直分量，单位可自由选择。

### 尺子是免费的吗？

当然。在线尺子完全免费，没有广告、无需注册、没有任何使用限制。

### 可以在不同边缘放置尺子吗？

可以。显示顶部、底部、左侧或右侧的尺子，或任意组合。使用工具栏中的边缘选择器即可设置。

# Keyword Guides

## 厘米尺子 — 屏幕上直接量厘米的在线尺子

URL: https://ruler.kiveo.org/zh/ruler-in-cm

想找一把厘米尺子？这款在线尺子直接在屏幕边缘显示厘米刻度，并带毫米细分刻线。用信用卡方式校准一次，这把厘米尺子就能长期保持精准。

### 如何使用厘米尺子

打开上方工具并选择厘米单位，屏幕的顶部和左侧边缘就会显示从角落开始计量的厘米尺子。想更精准，点击校准并选择信用卡方式，十秒即可让厘米尺子达到像素级精度。厘米尺子可以放在任意边缘：顶部、底部、左侧或右侧。

### 为什么用厘米尺子前要先校准

屏幕尺寸并非固定不变，厘米尺子的精度取决于 PPI 校准。自动识别可瞬间匹配 100+ 设备，屏幕对角线方式适合任何显示器，信用卡校准则让未知屏幕上的厘米尺子最精准。校准后，这款在线尺子的误差通常在 0.5mm 以内。

### 屏幕厘米对照参考

用下面的参考表检查厘米尺子是否准确：拿一把实体厘米尺贴在屏幕上对比几个刻度。如果数值有偏差，重新校准在线尺子，厘米刻度就会重新对齐。

厘米换算参考:
厘米 | 毫米 | 英寸
1 cm | 10 mm | 0.394 in
5 cm | 50 mm | 1.969 in
10 cm | 100 mm | 3.937 in
20 cm | 200 mm | 7.874 in
30 cm | 300 mm | 11.811 in

### 这把厘米尺子有多准？

信用卡校准后，厘米尺子在大多数屏幕上的误差约为 0.5mm。自动识别和对角线校准也能提供可靠的厘米尺子，误差通常在 1mm 以内。

### 可以用厘米尺子量真实物体吗？

可以 — 把实物贴在校准过的屏幕上（一张信用卡宽 8.56cm），厘米尺子就能读出它的真实尺寸。

### 手机上能用厘米尺子吗？

能。在手机上建议用信用卡方式校准，这样厘米尺子在小屏幕上也能保持精准。

## 英寸尺子 — 屏幕上直接量英寸的在线尺子

URL: https://ruler.kiveo.org/zh/ruler-in-inches

这把英寸尺子把英寸刻度贴在屏幕边缘，并带 1/16 英寸细分刻线。无论是测量屏幕元素、打印版式，还是贴在屏幕上的任何物体，都是同一款在线尺子，只需把单位切换到英寸。

### 如何使用英寸尺子

在工具栏选择英寸单位，英寸尺子就会出现在所选屏幕边缘，从左上角开始计量。整英寸有数字标注，半英寸刻线更长，最小刻度为 1/16 英寸。按 M 进入测量模式，英寸尺子还能验证任意两点之间的距离。

### 校准让英寸尺子更精准

未校准的屏幕会使用默认 PPI，在非标准显示器上英寸尺子会出现偏差。已知设备用智能自动识别，显示器可输入对角线快速校准，而信用卡校准能让英寸尺子最精准。校准结果保存在本地，下次访问自动复用。

### 英寸与厘米速查表

英寸尺子还能当换算器用：按 U 切换单位，同一测量值会立刻用厘米重新绘制。用下面的对照表，结合常见物体尺寸核对英寸尺子的读数。

英寸换算参考:
英寸 | 厘米 | 毫米
1 in | 2.54 cm | 25.4 mm
3 in | 7.62 cm | 76.2 mm
6 in | 15.24 cm | 152.4 mm
8.56 in（信用卡） | 21.74 cm | 217.4 mm
12 in | 30.48 cm | 304.8 mm

### 怎样才能得到真正准确的英寸尺子？

先校准 — 信用卡方式能让这把英寸尺子的误差控制在 0.5mm 左右，因为信用卡宽度正好是 3.37 英寸。

### 英寸尺子显示分数刻度吗？

刻度精确到 1/16 英寸。英寸尺子标注整英寸，测量读数则显示 4.75 in 这样的小数。

### 可以把英寸尺子切换成厘米吗？

可以，按 U 或点击单位按钮，同一款在线尺子会立即以厘米、毫米或像素重新绘制。

## 像素尺子 — 按像素测量屏幕

URL: https://ruler.kiveo.org/zh/pixel-ruler

像素尺子不需要卷尺：点击两个点，直接读出像素距离。这款在线尺子还会实时显示光标的像素坐标，UI 工程师不用打开设计工具就能核对间距、图标尺寸和布局留白。

### 像素尺子如何工作

选择像素单位后，边缘刻度全部切换为像素步长 — 主刻度每 100px、中刻度每 50px、细刻度每 10px。按 M 激活像素尺子的测量模式，点击两点，读数会给出 dx、dy 和对角线距离（单位 px）。光标读数则始终显示实时的 X/Y 像素坐标。

### 像素尺子与校准单位的区别

像素尺子永远精确，因为像素是屏幕的原生单位：一个 CSS 像素就是一个单位，无需校准。切换到厘米、毫米或英寸时会使用已保存的 PPI 校准，因此同一款在线尺子能对同一次测量同时输出 px 和真实世界单位。

### 设计师用像素尺子做什么

常见用途：检查按钮是否 44px 高、验证 8px 间距栅格、把线上页面与设计稿对比、测量图标点击区域。凡是需要打开设计标注工具的场合，像素尺子一次点击就能搞定。

### 像素尺子需要校准吗？

不需要。像素尺子按屏幕原生像素测量，天然就是准确的。在这款在线尺子里，校准只影响厘米、毫米和英寸模式。

### 像素尺子显示的是 CSS 像素还是设备像素？

它跟随浏览器坐标系（CSS 像素），与你写进 CSS 的数值一致。设备像素比会在校准过程中自动处理。

### 像素尺子免费吗？

免费 — 这款像素尺子完全免费，页面加载后可离线使用，本地只保存你的偏好设置。

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## Site Structure

- Home (EN): https://ruler.kiveo.org/en
- Home (ZH): https://ruler.kiveo.org/zh
- Contact: https://ruler.kiveo.org/en/contact
- Privacy Policy: https://ruler.kiveo.org/en/privacy
- Terms of Service: https://ruler.kiveo.org/en/terms
- Ruler in CM — Online Ruler Measured in Centimeters: https://ruler.kiveo.org/en/ruler-in-cm
- Ruler in Inches — Online Ruler Measured in Inches: https://ruler.kiveo.org/en/ruler-in-inches
- Pixel Ruler — Measure Your Screen in Pixels: https://ruler.kiveo.org/en/pixel-ruler
- Sitemap: https://ruler.kiveo.org/sitemap-index.xml