オンライン定規とは？

無料のオンライン仮想定規。画面上で直接物体のサイズを測定。cm とインチに対応。

Sometimes you need to measure a physical object but do not have a ruler or tape measure handy. Online Ruler turns your screen into a precise measurement tool by calibrating against a known reference object — like a credit card, a bill, or a piece of paper — to determine your screen's actual pixels per inch (PPI).

Calibration is the critical first step. Select a reference object from the list — credit card (standard 85.60mm × 53.98mm), A4 paper (210mm), US dollar bill (156mm), US quarter (24.26mm), 1 Yuan coin (25mm), or a custom object. Place the physical object flat against your screen and adjust the calibration slider until the on-screen box matches its real size. The calibration value is saved to your browser's local storage.

Once calibrated, switch to Caliper mode. Two vertical lines with red draggable handles appear on the ruler. Drag the handles to span the object you want to measure. The distance between the handles is shown simultaneously in centimeters (with millimeter precision), inches (with fractional display like 3 1/4"), and pixels.

Additional modes include Pointer mode with a crosshair for tracking position along the ruler, and Ruler view that shows a realistic dual-scale ruler with centimeter markings on the top edge and inch markings on the bottom edge. The ruler spans the full width of your screen for measuring objects up to the width of your display.