Angles in Year 6 — Types, Measuring & Calculating

Angles are one of the geometry topics that comes up every year in KS2 SATs. Children need to recognise different types, measure them accurately, and — most importantly — calculate missing angles using a few key rules. Here's everything your child needs.

Types of Angles

Acute angle — less than 90°. Think of a slightly open book.
Right angle — exactly 90°. The corner of a page. Marked with a small square.
Obtuse angle — between 90° and 180°. Wider than a right angle but not a straight line.
Straight angle — exactly 180°. A flat line.
Reflex angle — between 180° and 360°. More than half a turn.

SATs questions often ask children to identify the type of angle or to estimate whether an angle is acute or obtuse before measuring it.

Measuring Angles with a Protractor

Three steps to measure any angle:

Place the centre point of the protractor exactly on the vertex (the point of the angle).
Line up one arm of the angle with the zero line on the protractor.
Read the scale where the other arm crosses — but make sure you use the correct scale (inner or outer).

Quick check: if the angle looks acute (small), your reading should be less than 90°. If it looks obtuse (wide), it should be more than 90°. This catches most reading errors.

Angles in a Triangle (Sum = 180°)

The three angles inside any triangle always add up to 180°. This fact is a goldmine for finding missing angles.

A triangle has angles of 65° and 80°. Find the third angle.

65 + 80 = 145

Third angle = 180 − 145 = 35°

Angles on a Straight Line (Sum = 180°)

When two or more angles sit on a straight line, they add up to 180°.

Two angles on a straight line: one is 125°. Find the other.

Missing angle = 180 − 125 = 55°

Angles Around a Point (Sum = 360°)

All angles around a single point add up to 360° — a full turn.

Three angles around a point: 110°, 95° and x.

110 + 95 = 205

x = 360 − 205 = 155°

SATs-Style Example Question

“An isosceles triangle has one angle of 40°. What are the other two angles?”

Isosceles = two equal angles.

If 40° is the odd one out: the two equal angles share 180 − 40 = 140°

Each equal angle = 140 ÷ 2 = 70°

Watch out: this question could also mean 40° is one of the equal pair, giving 40°, 40° and 100°. The SATs will usually make it clear which case they mean, but it’s good to know both are possible.

Common Mistakes to Watch For

Reading the wrong protractor scale — using the outer scale when they should use the inner, or vice versa. Always estimate first.
Forgetting that triangles = 180° — some children try to measure the third angle instead of calculating it.
Mixing up 180° and 360° rules — straight line = 180°, around a point = 360°. Keep them separate.
Not marking right angles — if the question says “right angle”, use 90° in calculations, not an approximation.

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