Triangle area

Why is triangle area divided by two?

Make a copy of a triangle, rotate it, and join the pair. Together they form a parallelogram with the same base and perpendicular height, so one triangle occupies half its area.

Grades 5–6 · worked example · 3 practice checks

01

Recognize the problem first

  • The base can be any side, but the matching height must meet it at a right angle.
  • Two congruent triangles fill a parallelogram of area base × height.
  • Dividing by two accounts for using only one of the two matching triangles.
02

Work through one complete example

Question

A triangle has base 8 cm and perpendicular height 5 cm. Find its area.

  1. The matching parallelogram would have area 8 × 5 = 40 cm².
  2. One triangle is half of that parallelogram.
  3. Calculate 40 ÷ 2 = 20 cm².

AnswerThe triangle has area 20 cm².

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03

Common mistakes to catch

  • Using a sloping side instead of the perpendicular height.
  • Adding base and height before dividing by two.
  • Forgetting square units in the answer.
04

Try three quick checks

01

Base 10 cm, height 6 cm.

Show answer30 cm²
02

Base 7 m, height 4 m.

Show answer14 m²
03

Area 24 cm², base 8 cm. Find the height.

Show answer6 cm
05

Turn the method into practice

Generate a fresh worksheet when the learner can explain the method. Keep the answer key separate during independent practice.

Area and perimeter worksheet generatorChoose the range, difficulty, question count, and print layout.Area and perimeter worksheetsPrint free area and perimeter worksheets for grades 3–6, including missing sides, triangles, and composite L-shapes, with worked answers.

Related visual guides

Area or perimeter: how to tell which one you need→Find a missing side from area or perimeter→How to find the area of a composite shape→

Content reviewExamples and explanations reviewed 29 September 2026. Found a problem? Send a correction

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