About Angle Finder Protractor

It began with a phone held against a door frame and a question that should have been easy: is this corner square? A paper protractor from a school drawer would have answered it, but there was no paper to hand, and every app I tried wanted a subscription before it would show an angle. That evening I drew a protractor arc on an HTML canvas and dragged two handles onto a photo of the frame. It was wrong by about a degree, and completely addictive.

Each version answered a complaint from real use. Photo mode arrived because a camera cannot measure a corner you cannot reach. The gyroscope mode arrived because phones already contain the sensor a digital level needs, and nobody should have to pay for a bubble. The calculators arrived because the number you measure and the number you need for the cut are rarely the same thing - a corner angle becomes half of it on the saw, a slope becomes a pitch, degrees become radians. The measurement history arrived after a page of readings was lost to a locked screen.

Everything runs in your browser. Camera frames are drawn to a canvas, photos are decoded with a local file picker, measurements sit in your browser storage, and the CSV export is assembled on your machine. There is no server component waiting to receive your numbers, because there is nothing on the other end to receive them.

It is free, with no account, no paywall and no feature held back for a subscription. The interface is available in nine languages, and every number is formatted the way each language writes it - a comma or a decimal point appears where it belongs without you configuring anything.

And it is honest about its limits. Where a measurement is approximate, the page says so. A photograph taken from an angle will not give a true reading no matter how clever the overlay is, and a phone sensor is a convenient field check rather than a calibrated instrument. Telling you that is more useful than a confident number you would build a roof on.

Plain HTML, CSS and JavaScript behind a small static build - no framework runtime in the measurement path. The protractor is drawn on a single canvas with the 2D API, the camera arrives through WebRTC, tilt comes from the DeviceOrientation API, and every number on the screen is formatted through Intl.NumberFormat, so the same code writes a decimal comma where Spanish readers expect one and a decimal point where English readers expect it.

The calculators and guides grew out of the same workflow: measure, then convert, then cut. If something here is wrong, confusing or missing the unit you need, the contact page reaches me directly - the useful bug reports are the ones with a screenshot attached.