Online Ruler — Actual Size Ruler in cm, mm & Inches

Online Ruler is a free set of measuring tools that run entirely in your browser. Its actual-size screen ruler shows centimeter, millimeter and inch scales, and a calibration step fixes the usual problem of on-screen rulers being wrong on phones and high-DPI displays: match the outline to an ISO/IEC 7810 ID-1 bank card (85.60 x 53.98 mm) or enter your screen diagonal.