Right Angle (90-Degree Angle): Definition, Examples, Chart, and Practice

What is a right angle?

A right angle is an angle that is exactly 90°.

A right angle is also called a 90-degree angle. Both names mean the same thing.

It looks like a square corner. You can see right angles in corners of books, doors, windows, tiles, and many boxes.

In a diagram, a right angle is often marked with a small square in the corner.

Right angle rule

Use this rule to check a right angle.

A right angle = 90°

If an angle is exactly 90°, it is a right angle. If it is less than 90° or more than 90°, it is not a right angle.

Right angle chart

This chart shows how a right angle compares with other common angle types.

A right angle is not a range. It is one exact size: 90°.

How to spot a right angle

Look for a corner that makes an L shape.

Look for a small square mark inside the corner. That square mark means the angle is 90°.

You can also use the corner of a ruler, a book, or a sheet of paper to check if an angle is a right angle.

Worked example

Problem: A diagram shows one angle marked with a small square. What type of angle is it?

Step 1: The small square tells us the angle is 90°.

Step 2: An angle that is exactly 90° is a right angle.

The angle is a right angle.

Right angles in shapes

A square has 4 right angles.

A rectangle also has 4 right angles.

Some triangles have 1 right angle. A triangle with 1 right angle is called a right triangle.

A shape can have no right angles, one right angle, or many right angles.

Right angle vs. other angles

Acute angle: less than 90°. It is smaller than a right angle.

Right angle: exactly 90°. It makes a square corner.

Obtuse angle: more than 90° but less than 180°. It is wider than a right angle.

Straight angle: exactly 180°. It makes a straight line. You can compare all of these in the types of angles chart.

How to draw a right angle

Step 1: Draw one straight ray across the page.

Step 2: From the same corner point, draw another ray straight up.

Step 3: Add a small square in the corner to show it is 90°.

The two rays should make an L shape. If that 90° corner is split into two smaller angles, those two angles can be complementary angles.

Real-life right angle examples

The corner of a book is usually a right angle.

The corner of a door or window can be a right angle.

Floor tiles often have right angles at their corners.

Many boxes, desks, shelves, and picture frames have right angles. Lines that meet at this square corner are perpendicular, unlike parallel lines, which never meet.

Common mistakes

Do not call every corner a right angle. A right angle must be exactly 90°.

Do not call an angle right just because it looks close. If it is 89° or 91°, it is not a right angle.

Do not confuse the square marker with a tiny square shape. The marker means the angle is 90°.

Quick practice

1. Is 90° a right angle? Yes, because a right angle is exactly 90°.

2. Is 75° a right angle? No. It is less than 90°, so it is acute.

3. Is 110° a right angle? No. It is more than 90°, so it is obtuse.

4. How many right angles does a rectangle have? A rectangle has 4 right angles.