Acute Angles – Smaller Than a Right Angle

An acute angle is any angle that measures more than 0° and less than 90° – in other words, it's “sharper” or narrower than a right angle. The word “acute” comes from the Latin acutus, meaning “sharp” or “pointed” – the same root that gives us words like “acute pain” (sharp pain).

Acute angles are the first of the five angle-size categories you'll meet in this section (acute, right, obtuse, straight, reflex), and they're the natural starting point since they're the smallest non-zero angle type.

Recognising an Acute Angle

Real-Life Application

• Roof pitches: steep roof designs often use acute angles at the peak.
• Scissors and pliers: tools often open to acute angles for precise, narrow cuts or grips.
• Arrowheads: the sharp tip of an arrow or dart forms an acute angle.

Key Takeaways

Practice: Acute Angles