Straighten

Level the horizon, fix perspective, measure on a photo.

What it does

Three jobs on a photo, on your device (nothing is sent).

Horizon: drag the ends of the line onto the horizon, or onto something that should be vertical (a wall, a pole). The photo turns by that angle and is cropped so no corner is empty. Fine-tune with the slider.
Perspective: place the 4 corners on something that is really a rectangle (a document, a painting, a facade, a screen): the photo is flattened as if seen from the front. Proportions: estimated from the sides (Auto), or a known format.
Measure: put the orange line on something of known length (a bank card is 85.6 mm wide), type its length, then drag to measure anything else. It is only right in the same flat plane as the reference: flatten the perspective first for best results.

Free, no account, nothing is sent: it runs in your browser, even offline.