Units of Measurement (cm and mm) worksheet - Free Printable

Let's solve this step by step.

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Part 1: Choose the best unit of measurement (cm or mm) for each item

We need to decide whether centimeters (cm) or millimeters (mm) is the most appropriate unit for measuring each object.
Remember:
- 1 cm = 10 mm
- mm is used for smaller, more precise measurements.
- cm is used for larger everyday objects.

Let’s go through each:

| Item | Best Unit | Reason |
|------|-----------|--------|
| Finger nail | mm | Very small; thickness and length are best measured in millimeters. |
| Pencil | cm | A typical pencil is about 15–20 cm long — too long for mm practicality. |
| A Pea | mm | Small object; about 5–10 mm in diameter. |
| Sheet of paper | cm | Standard size is 21.6 cm × 27.9 cm (A4), so cm is suitable. |
| A Peanut | mm | Small, about 10–15 mm long. |
| A Staple | mm | Very small; only a few millimeters long. |
| Pencil point | mm | The tip is tiny; precision needed → mm. |
| Cup | cm | Height and diameter are around 10–15 cm. |
| Envelope | cm | Size is typically 23 cm × 11 cm or similar. |
| Battery | cm | AA battery is about 5 cm long; cm is convenient. |
| Pencil top eraser | mm | Small, usually about 10–15 mm in diameter. |
| Spoon | cm | A teaspoon is about 12–15 cm long. |

✔ So the correct choices are:

- Finger nail → mm
- Pencil → cm
- A Pea → mm
- Sheet of paper → cm
- A Peanut → mm
- A Staple → mm
- Pencil point → mm
- Cup → cm
- Envelope → cm
- Battery → cm
- Pencil top eraser → mm
- Spoon → cm

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Part 2: Convert centimeters to millimeters

Use the conversion:
1 cm = 10 mm
So multiply the number of centimeters by 10.

1. 4 cm = ? mm
→ 4 × 10 = 40 mm

2. 7 cm = ? mm
→ 7 × 10 = 70 mm

3. 19 cm = ? mm
→ 19 × 10 = 190 mm

4. 123 cm = ? mm
→ 123 × 10 = 1230 mm

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✔ Final Answers:

#### Best Units:
- Finger nail → mm
- Pencil → cm
- A Pea → mm
- Sheet of paper → cm
- A Peanut → mm
- A Staple → mm
- Pencil point → mm
- Cup → cm
- Envelope → cm
- Battery → cm
- Pencil top eraser → mm
- Spoon → cm

#### Conversions:
- 4 cm = 40 mm
- 7 cm = 70 mm
- 19 cm = 190 mm
- 123 cm = 1230 mm

Let me know if you'd like this formatted as a printable answer sheet!