Grade 6 Mathematics Measurements – Length Notes
Mathematics — Measurements
Subtopic: Length (for age 11 — Kenyan context)
What is length?
Length is how long something is from one end to the other. We measure length to know size, compare objects or find distance between two places.
Common units of length (metric system used in Kenya)
- Millimetre (mm) — small parts (e.g., thickness of a coin)
- Centimetre (cm) — notebook lines, small objects
- Metre (m) — height of a door, length of a classroom
- Kilometre (km) — distances between towns (e.g., Nairobi to Mombasa ≈ 480 km)
Abbreviations: mm, cm, m, km
How to convert between units
- 10 mm = 1 cm
- 100 cm = 1 m
- 1000 m = 1 km
To change to a bigger unit: divide. To change to a smaller unit: multiply.
- Convert 250 cm to metres: 250 ÷ 100 = 2.50 m
- Convert 3.2 km to metres: 3.2 × 1000 = 3200 m
- Convert 45 mm to cm: 45 ÷ 10 = 4.5 cm
Measuring tools
- Ruler — usually marked in cm and mm (use for short lengths)
- Tape measure — for longer pieces (e.g., desks, doors)
- Trundle wheel or measuring wheel — for long distances on the ground
How to measure correctly (simple steps)
- Place the start of the ruler/tape at one end of the object (at 0).
- Stretch the tape straight along the object without sagging.
- Read the number at the other end to the nearest mm or cm, depending on the tool.
- If the object is longer than the ruler, mark one end, move the ruler and add the measures.
Quick estimating tips
- An ordinary classroom desk is about 1 m long.
- Your textbook height is about 20–30 cm.
- A door is about 2 m tall.
Simple visual: a 15 cm ruler (not real size)
Worked examples
- Mary measures a table and finds it is 120 cm long. What is the length in metres?
120 ÷ 100 = 1.20 m. So the table is 1.20 m long.
- A footbridge is 2.5 m long. How many centimetres is it?
2.5 × 100 = 250 cm.
- The distance from town A to town B is 36 km. Express this in metres.
36 × 1000 = 36 000 m.
Practice questions (try these)
- Convert 760 mm into cm and mm (show answer as x cm y mm).
- A classroom's length is 8 m and width is 6 m. What is the total length around (perimeter)?
- If a rope is 1250 cm long, how many metres is it?
- Estimate: Is a pen longer than 10 cm? (yes/no) — explain briefly.
- 760 mm = 76 cm 0 mm (or simply 76 cm).
- Perimeter = 2 × (8 + 6) = 2 × 14 = 28 m.
- 1250 cm = 1250 ÷ 100 = 12.50 m (or 12.5 m).
- Most pens are longer than 10 cm, so answer: yes — because a typical pen is about 14 cm long.
Practical school activity
In groups, measure: one desk, the classroom chalkboard, and the playground length. Record in cm and m. Compare results and discuss which unit is best for each measurement.
Keep practising measuring with a ruler and tape. Good measuring helps in real life — building, mapping and travelling across Kenya.