¿Qué es Regla online?
An online ruler is a screen-based measurement tool that displays a calibrated ruler at real-world scale on your monitor. By calibrating to your screen's pixel density (PPI — pixels per inch), the ruler shows markings that represent actual inches or centimeters, allowing you to measure flat objects placed on your screen without a physical ruler. Our online ruler works on any screen — laptop, desktop, or tablet — and supports both imperial and metric units.
The tool requires a one-time calibration using a known-size object, most reliably a credit card (85.6mm × 53.98mm per ISO/IEC 7810 standard). Once calibrated, the ruler persists in your browser's local storage until you recalibrate or clear browser data. It's particularly useful for quick measurements when a physical ruler is not at hand, for verifying print-ready document sizes, and for measuring UI elements against their design specifications.
The online ruler does not replace a physical ruler for precision work, but fills a practical gap: it is always available in any browser, costs nothing, and is accurate enough for most everyday measurement needs. Design professionals, students, remote workers, and anyone who works primarily at a computer can benefit from having a reliable measurement tool permanently accessible in their browser.
Casos de uso
Aquí tienes las formas más comunes en que la gente usa Regla online todos los días.
Quick Object Measurements
When you need a quick measurement and cannot find a physical ruler, place the flat object directly on your screen and read the measurement. Practical uses: checking if a photo is standard size before ordering prints, measuring a business card to verify it meets standard specifications, checking if a printed document template will fit correctly, or measuring a component that arrived without specifications.
Design Mockup Scale Verification
When working in design tools like Figma or Adobe XD, verify that elements are at the correct physical scale by comparing the ruler to on-screen dimensions. A UI element designed to be 44px tall (the minimum touch target size per Apple HIG) should measure approximately 15.5mm on a properly calibrated screen at 100% zoom. This helps catch scale errors before sending designs to developers or to print.
Print-Ready Document Checking
Before sending a document to print, verify that the page size and margins appear at their intended physical dimensions when the ruler is calibrated and the document is at 100% zoom. A standard letter page should measure exactly 8.5 × 11 inches. If it measures differently, the document zoom level or page size settings need correction. This catches print size errors before wasting paper and printing costs.
Remote Work and Virtual Collaboration
In remote assistance scenarios, you can guide someone to use the online ruler to measure a physical object and report the measurement without needing a physical ruler. Particularly useful for home office setup measurements, furniture clearance checks, and technical support for physical hardware where dimensions need to be verified without a specialist present.
Ejemplos
Measuring a Business Card
Standard business card: 3.5 × 2 inches (88.9 × 50.8mm). Place on calibrated ruler to verify.
Ruler reads 88.9mm — matches standard specification Checking Photo Print Size
Place a 4×6 photo at 100% zoom on screen and verify with the ruler.
Should read 4 inches (101.6mm) wide when at true size Regla online frente a Physical Ruler
When to use the online ruler versus a physical ruler.
| Característica | Toolorah | Physical Ruler |
|---|---|---|
| Always available | Yes — any browser | Only if you own one |
| Accuracy | ±1–2mm after calibration | ±0.5mm or better |
| Requires calibration | Yes (one-time) | No |
| Maximum length | Screen width (~25–50cm) | Length of the ruler |
| Works on curved surfaces | No | With flexible rulers |
| Cost | Free | $1–$20+ |
Consejos para usar Regla online
- Use a standard credit card (85.6mm × 53.98mm) for calibration — it is a global standard dimension you always have available.
- The ruler is only accurate on flat, non-curved screens. Curved monitors and CRT monitors will produce distorted measurements.
- Windows display scaling (125%, 150%) and macOS display scaling affect calibration — recalibrate after changing display scaling settings.
- For precision measurements (±0.5mm or better), always use a physical ruler or digital calipers.
- The ruler measures horizontally. For vertical measurements, rotate the object 90° or use the tool's vertical ruler mode if available.
Preguntas frecuentes
How do I calibrate the online ruler?
The most reliable calibration method uses a standard credit or debit card. All credit cards worldwide conform to ISO/IEC 7810 ID-1: 85.60mm × 53.98mm (3.370 × 2.125 inches). Place your card on the screen aligned with the ruler's starting point, then drag the calibration handle until the ruler length matches the card's width (85.6mm). Click Save. The calibration is stored in your browser's localStorage and persists across sessions. Alternative: enter your monitor's diagonal size and resolution for a calculated calibration (less accurate due to screen border and pixel density variations).
Is an online ruler as accurate as a physical ruler?
No. Physical rulers are manufactured to tolerances of ±0.5mm or better, with no dependence on calibration. An online ruler's accuracy depends on the calibration quality, screen pixel density uniformity, display scaling settings, and browser zoom level. After careful calibration with a credit card, expect accuracy of ±1-2mm — adequate for quick reference measurements but not for precision work. For carpentry, sewing, machining, or any application where ±1mm matters, use a physical ruler, tape measure, or calipers.
Why does calibration need to be done per device?
Every screen has a unique physical pixel density (PPI — pixels per inch). A 24-inch 1080p monitor has approximately 92 PPI. A 27-inch 4K monitor has approximately 163 PPI. A 13-inch MacBook retina display has approximately 227 PPI. Without knowing the actual PPI, the ruler cannot calculate the physical size of a pixel. Calibration establishes this relationship for your specific screen. If you use the ruler on a different monitor, you need to recalibrate for that screen.
Does it work on mobile devices?
The ruler works on tablet screens (iPad, Android tablets) and can give approximate measurements, but accuracy is lower because phone and tablet screens vary more widely in pixel density and are often used at varying distances and orientations. For mobile use, calibrate carefully using the credit card method and use results as approximations only. Curved-screen smartphones and very small screens (under 5 inches) are not well-suited for the online ruler.
What if my screen has non-standard DPI settings?
Windows display scaling (125%, 150%, 175%) and macOS display scaling affect how browsers render pixels. The browser reports a different device pixel ratio depending on the scaling setting, which changes the effective PPI that the ruler uses. If you change display scaling after calibrating, recalibrate the ruler. The credit card calibration method self-corrects for display scaling because it measures against a known physical dimension rather than calculating from reported PPI.