📏 在线尺子（屏幕实际尺寸 1:1 刻度尺）Online Ruler (Actual Size)
在屏幕上显示 1:1 真实尺寸的刻度尺，支持厘米/毫米、英寸和像素，拖动红线即可测量长度；用银行卡（85.6 毫米）或屏幕尺寸+分辨率校准后，测量小物件、纸张、戒指尺寸、螺丝等误差很小，校准结果自动保存。A real-size ruler on your screen in cm/mm, inches and pixels — drag the red line to measure. Calibrate with a bank card (85.6 mm) or your screen size and resolution for accurate measurements of small objects, paper, rings or screws; calibration is saved.
📐 校准（让尺子和实物 1:1）Calibrate to real size
方法一：把一张银行卡/身份证（标准宽度 85.6 毫米）的长边贴在屏幕上，拖动滑块直到下面的卡片和实物一样宽。Method 1: hold a bank card (standard width 85.6 mm) against the screen and drag the slider until the box below matches the card.
方法二：输入屏幕对角线尺寸和分辨率自动计算。Method 2: enter the screen diagonal and resolution.
使用说明与常见问题How-to & FAQ
「在线尺子（屏幕实际尺寸 1:1 刻度尺）」是什么？What is the Online Ruler (Actual Size)?
在屏幕上显示 1:1 真实尺寸的刻度尺，支持厘米/毫米、英寸和像素，拖动红线即可测量长度；用银行卡（85.6 毫米）或屏幕尺寸+分辨率校准后，测量小物件、纸张、戒指尺寸、螺丝等误差很小，校准结果自动保存。A real-size ruler on your screen in cm/mm, inches and pixels — drag the red line to measure. Calibrate with a bank card (85.6 mm) or your screen size and resolution for accurate measurements of small objects, paper, rings or screws; calibration is saved.
如何使用「在线尺子（屏幕实际尺寸 1:1 刻度尺）」？How do I use the Online Ruler (Actual Size)?
先校准：把银行卡长边贴在屏幕上，拖动滑块直到虚线框和卡一样宽，点“保存校准”。然后把物体放在尺子上，从 0 刻度对齐，拖动红线到物体另一端读数即可。Calibrate first: hold a bank card to the screen, drag the slider until the dashed box matches its width and press Save. Then align the object with 0 and drag the red line to its other end to read the length.
为什么不校准就不准？Why calibrate?
不同设备屏幕像素密度不同，浏览器无法直接得知屏幕的物理尺寸，默认按 96 DPI 估算，在手机和高分屏上会有偏差。用银行卡校准一次即可精确到约 0.5 毫米。Screens have different pixel densities and browsers cannot know the physical size, so the default 96 DPI guess is off on phones and high-DPI screens. One bank-card calibration makes it accurate to about 0.5 mm.
能测戒指尺寸吗？Can I measure ring size?
可以：把戒指放在尺子上量内径，或用一条纸条绕手指一圈后量长度（周长），再查戒指尺码对照表。Yes — measure the inner diameter on the ruler, or wrap a paper strip around your finger and measure its length (circumference), then check a ring size chart.
「在线尺子（屏幕实际尺寸 1:1 刻度尺）」免费吗？文件会上传吗？Is the Online Ruler (Actual Size) free? Are my files uploaded?
「在线尺子（屏幕实际尺寸 1:1 刻度尺）」完全免费，无需注册。你输入的内容只保存在本机浏览器里（方便下次继续），不会上传到任何服务器。The Online Ruler (Actual Size) is free with no sign-up. What you enter stays in this browser only (so you can continue later) and is never uploaded to any server.