Frequently Asked Questions

ScreenTools is a free collection of browser-based utilities for people who work with screens: device specs, dead pixel testing, aspect ratio calculations, pixel conversion, screen-size math, and PPI/DPI calculations. The tools run in your browser with no account or install.

Yes. ScreenTools is free to use, with no sign-up, hidden fees, or premium tier. The linked sister-site measurement tools are free as well.

No. ScreenTools works entirely in your web browser. Just open screentools.online and choose the utility you need. No app, plugin, or extension is required.

Any device with a modern web browser is supported: iPhones, Android phones, iPads, tablets, laptops, desktops, monitors, and TVs. The device-specs database includes 69+ verified devices, and calculators also accept custom inputs.

No tool inputs or measurement results are uploaded for calculation. Most settings stay in your browser storage. We use Google Analytics for anonymous, aggregate page view statistics only.

ScreenTools calculators are math-based and return results from the numbers you enter. Physical on-screen measurement accuracy depends on display calibration, so those workflows open on our sister site where the ruler can be calibrated against a known reference object.

You need calibration only when a tool must display a physical real-world size on your screen. Calculators such as PPI, aspect ratio, pixel conversion, and screen-size math do not need calibration.

The sister-site ruler supports common reference objects such as credit/debit cards, selected coins, and A4 paper. A standard credit card is usually the easiest and most reliable option.

Browsers report layout dimensions in CSS pixels, not exact physical pixels. Without knowing the display's real PPI, any physical ruler can only estimate. Calibration establishes the true pixels-per-millimeter ratio.

They work best on flat screens. Curved displays can introduce small edge errors, so measure near the center and verify critical dimensions against a physical reference.

A screen-based ruler can only show the physical length available on the display. For longer objects, measure in sections or use the printable-ruler workflow on the sister site.

The sister-site protractor shows two draggable rays from a center point. Move either ray to match the lines you are checking, and the angle between them updates immediately.

Yes. The protractor supports snapping to common increments such as 1°, 5°, 15°, and 45° so you can set exact construction or design angles quickly.

The protractor shows the smaller angle by default. For a reflex angle above 180°, subtract the displayed angle from 360°.

The spinner uses browser-side pseudo-randomness for fair everyday decisions such as classroom picks, team assignments, and quick choices. It is not intended for cryptographic or regulated random draws.

You can add practical everyday lists such as names, tasks, prizes, or choices. Very large lists may become harder to read on the wheel, so shorter labels work best.

If weighted options are enabled in the spinner, higher-weight entries appear more often in the selection pool. Use equal weights when every option should have the same chance.

Spinner state is kept in your browser when available, so recent options can survive a refresh on the same device. Clearing browser data removes that local history.

ScreenTools is available in 20 languages: English, Chinese (Simplified and Traditional), Japanese, Korean, Spanish, French, German, Hindi, Indonesian, Vietnamese, Turkish, Thai, Malay, Croatian, Czech, Romanian, Serbian, Slovenian, and Filipino.

Some tools keep working after the page has loaded, but an initial connection is required to load the site. Full offline/PWA behavior may vary by browser.

All modern browsers are supported, including Chrome, Firefox, Safari, Edge, and their mobile versions. JavaScript must be enabled.