Online Protractor
Last updated: 2026-10-15
No protractor? Measure any angle from 0° to 180° right on the screen. Place the vertex at the centre, align the 0° baseline with one side, then rotate the blue arm to read the angle.
What this online protractor does
This is a free online protractor for measuring angles on your screen. Drag the protractor over the shape you want to measure, set its centre point on the vertex of the angle, and line the 0° baseline up with one side. The blue arm marks the other side, and the reading at the top of the card updates as you move it. You can also drag the arm on its own to match an angle that is already drawn.
There is nothing to install and nothing to print. It is most useful for angles that already exist on screen, such as a screenshot, a drawing, a photo or a design file, where a paper protractor would be awkward to hold in place.
How to measure an angle with the on-screen protractor
Use the on-screen protractor like a physical one — the key is to align the centre and the 0° baseline first.
Place the vertex
Put the vertex of the angle you're measuring at the protractor's centre point.
Align the 0° baseline
Line the 0° baseline up with one side of the angle.
Read the angle
Drag the blue arm until it meets the other side, then read the value.
How to read a protractor
A semicircular protractor prints two runs of numbers that count in opposite directions. Reading the wrong run is the most common beginner mistake.
| Scale | Starts at 0° | Numbers increase |
|---|---|---|
| Inner scale | Right end | Right to left |
| Outer scale | Left end | Left to right |
To pick the right run, look at which way the angle opens. A physical protractor is used with its 0° line sitting on one side of the angle: whichever end that is, you count outwards from that end and read the number the other side crosses. Many shop protractors tint the two runs in different colours so you can tell them apart at a glance.
The on-screen protractor prints both runs, exactly like a physical one: the outer scale in grey, the inner scale in blue. You still never have to pick between them, because the arm gives a single live reading — the number the arm points at is the one to use, on whichever scale you prefer to read.
Types of angles
| Name | Measure |
|---|---|
| Acute | Less than 90° |
| Right | Exactly 90° |
| Obtuse | More than 90°, less than 180° |
| Straight | Exactly 180° |
| Reflex | More than 180°, less than 360° |
| Full | Exactly 360° |
Measuring a reflex angle needs a full-circle (360°) protractor. This on-screen tool covers the everyday half-circle range, 0° to 180°, which is where most school, drawing and shop measurements sit.
Common angles and where they show up
| Angle | Where you meet it |
|---|---|
| 30° | One corner of a 30/60 set square; half of an equilateral triangle's corner (60°) |
| 45° | Miter cuts on trim and picture frames; the 45-45-90 set square |
| 60° | Every corner of an equilateral triangle; the 30/60 set square |
| 90° | An inside wall corner, an L bracket, the corner of a Letter sheet |
| 120° | Each interior corner of a regular hexagon |
| 135° | Interior corner of a regular octagon; many miter joints |
| 180° | A straight line, the flat edge of a rule |
In woodworking and trim work, 45° and 135° are the usual miter angles, because two 45° cuts meeting edge to edge close a 90° corner. Framing and casework lean on 90°.
Measuring angles already on your screen
A paper protractor can only measure a real corner you can press it against. The on-screen version also measures angles that arrive as an image.
A screenshot. Open or paste the image beside the protractor, set the centre on the vertex, and drag the arm until it meets the second line.
A map bearing. Turn the map so north points up, then measure the angle of the line between two points to read its bearing.
A photo. Photograph the object and measure on the picture. This suits corners you cannot reach, such as ceiling lines, a roof slope or a joint high on a wall.
A design file. Check the tilt of a vector shape, the slant of an interface element, or any angle an exported drawing cannot spell out.
Great for quick measurement and checking of common plane angles.
An angle is a geometric relationship, so the screen size never changes the reading.
Need a physical tool? Print the protractor on the page at 100% scale.
Online protractor vs a printed protractor
Print the protractor and press it on the sheet. You can mark points at any degree along the printed scale.
Keep it on screen. Screenshots, maps and photos are measured directly, with no printing or trimming first.
Read the angle online, then print the same page when you want a tool you can hold against paper.
How accurate is the online protractor
Accuracy rests on how well you line the protractor up, not on the screen. On a typical display, one pixel of misalignment along the arm is worth roughly 0.2°, and in careful use the total alignment error usually stays within about 1°.
That is enough for homework, sketching, layout and general shop measurement. Where a job calls for tighter tolerances, use a physical protractor or a dedicated measuring instrument.
Printable protractor
Choose 100% or "actual size" when printing, and turn off "fit to page". After printing, you can check a known length on the page with a real ruler.
Frequently asked questions
Does the online protractor need calibration?
No. An angle doesn't depend on how long 1 mm is on screen, so there's no physical-size calibration like the online ruler needs.
Can I use the protractor on a phone?
Yes. As long as the on-screen protractor and the angle you're measuring have enough room, it works; a larger screen usually makes alignment easier.
Why is my angle reading wrong?
The most common cause is the angle's vertex not being at the centre, or the 0° baseline not lined up with one of the sides.
Can the online protractor be printed?
Yes. Print at 100% or actual size and don't choose "fit to page" or any automatic scaling.