TheProtractor.com · Free Browser Angle Instrument
Protractor – Free Online Protractor & Digital Protractor Tool
Welcome to TheProtractor.com, the precision online protractor and digital protractor built for students, teachers, architects, and makers. Whether you need a protractor online to measure angles on an uploaded protractor image, a full-screen mobile edge gauge, or a high-resolution printable protractor, our free online protractor tool delivers instant sub-degree accuracy in your browser.
What Is a Protractor? (Protractor Definition & Scale Guide)
If you are asking what is a protractor, the standard protractor definition describes a semicircular (180°) or circular (360°) geometric instrument graduated in degrees for measuring and constructing plane angles. Our interactive protractor tool upgrades the traditional plastic protractor into a versatile digital protractor featuring both an outer counterclockwise scale (0° to 180°) and an inner clockwise scale (180° to 0°), plus a full 360° circle for reflex angles. Unlike basic tools people find when searching protractor.com or theprotractor.com, our workspace computes live vector angles in Degrees (°), Radians (rad), and Gradians (gon) with complementary, supplementary, and explementary readouts.
How to Use a Protractor to Measure Angles
Learning how to use a protractor—or how to use protractor scales on a computer or phone—takes four steps:
Align the Center Vertex
Drag the center origin of the online protractor directly onto the vertex where the two lines meet. Resize the protractor anytime using the size slider or rim handles (`⤢`).
Set the 0° Baseline (Ray A)
When learning how to use a protractor to measure angles, align the 0° baseline first. Drag handle A or rotate the protractor (`↻`) so the baseline sits flush along one line.
Measure with the Target Arm (Ray B)
Drag handle B onto the second line. Read the degree mark where Ray B crosses the scale—our online protractor tool displays the exact angle automatically.
Measure on Photos or Physical Edges
Click Upload Image to measure on a photo, or tap Full Screen and dock to the Bottom, Top, Left, or Right edge to place your phone against a real object.
Measure on Any Protractor Image & Export a Printable Protractor PNG
Click Upload Image (or drag and drop a file) to load any JPG, PNG, or WEBP protractor image background. Uploaded photos automatically fit your canvas and can be moved or resized from any corner independently of the protractor. Need a printable protractor or transparent protractor PNG? Click Export in the toolbar to download a 1× or 2× retina protractor printable graphic or annotated diagram—processed 100% locally in your browser with zero server uploads.
Frequently Asked Questions About Protractors
What is a protractor?
A protractor (also written "what's a protractor") is a semicircular or circular measuring instrument marked in degrees (0° to 180° or 0° to 360°) that is used to measure and draw angles. It is a basic geometry tool used in math classes, drafting, engineering, carpentry, and navigation.
What is a protractor used for?
A protractor is used to measure angles, draw angles of an exact size, and check whether corners are square or match a design. Students use it in geometry, while architects, engineers, woodworkers, and surveyors use it to lay out and verify angles.
What does a protractor look like?
A typical protractor is a flat, transparent, half-circle (180°) piece of plastic with a straight baseline, a center point or origin mark, and two rows of degree numbers around the curved edge. Full-circle 360° protractors also exist. TheProtractor.com shows both styles on screen.
How do you use a protractor to measure angles?
1) Place the center point on the vertex (corner) of the angle. 2) Align the 0° baseline with one arm of the angle. 3) Follow the scale that starts at 0° along that arm. 4) Read the value where the other arm crosses the scale. If the arm is too short to reach the scale, extend it with a ruler first. If the angle looks acute (under 90°) use the smaller number; if it looks obtuse (over 90°) use the larger one.
How do you read a protractor?
Most protractors have two scales, an outer and an inner one, running in opposite directions. Begin at the 0° mark that sits on your baseline arm and follow that scale to the second arm. If the baseline arm points right, read the scale that starts at 0° on the right; if it points left, use the scale starting at 0° on the left. Then check that the answer makes sense: acute angles are under 90° and obtuse angles are over 90°.
How do you use a protractor online?
Open TheProtractor.com in any browser. Drag the protractor's center onto the vertex of your angle, rotate Ray A to match one line, and drag Ray B to the other line. The angle appears live in degrees, radians, or gradians. You can also upload an image to measure on a photo, or dock the protractor to a screen edge on a phone to measure real objects. It's free and nothing is uploaded to a server.
How do you measure angles without a protractor?
You can measure angles without a protractor in several ways: (1) use a free online protractor like TheProtractor.com; (2) fold paper and compare against known angles such as 90° (a corner) and 45° (a diagonal fold); (3) use a set square (45° or 30°/60°); (4) measure side lengths and compute the angle with trigonometry, for example angle = arctan(opposite ÷ adjacent); or (5) use a smartphone level or angle-finder app.