Slide 1 of 7 · Settling starter · Art · Year 8
5 minutesUsing Scale Factors and Proportion to Plan a Community Mural
When public artists paint a community mural on a library wall, they scale up an A4 sketchbook grid so every motif keeps its exact proportion. Today you will scale a 24 cm by 15 cm design up to a 4.8 m by 3.0 m wall in Aberdare.
While the register is called: write your name, class and date on your worksheet, then read Section 1 on the stimulus sheet and answer the starter question in rough.
Starter question: In the sketchbook grid, 1 cm represents 0.2 m (20 cm) on the real library wall. Check that multiplying 24 cm by 0.2 m and 15 cm by 0.2 m gives the exact wall dimensions of 4.8 m by 3.0 m.
Slide 2 of 7 · Today’s brief and key formulas · Art · Year 8
5 minutesLinear scale factor vs area and paint coverage
When you enlarge a 2D artwork by a linear scale factor of 20, every length becomes 20 times bigger, and every 1 cm by 1 cm square becomes a 0.2 m by 0.2 m square on the wall.
| Quantity | Sketchbook (A4 grid) | Real Aberdare library wall |
|---|---|---|
| 1 grid square side length | 1 cm | 1 cm × 20 = 20 cm = 0.2 m |
| Whole mural dimensions | 24 cm × 15 cm (360 squares) | 4.8 m × 3.0 m = 14.4 m2 |
| 1 grid square area | 1 cm × 1 cm = 1 cm2 | 0.2 m × 0.2 m = 0.04 m2 |
| 1 tin of masonry paint (750 ml) | Covers 8 m2 per litre (1,000 ml) | 0.75 litres × 8 m2 = 6.0 m2 for 1 coat (or 3.0 m2 for 2 coats) |
Slide 3 of 7 · Step 1: Scale up the 5 mural motifs · Art · Year 8
10 minutesStep 1: Calculate full-size dimensions for the 5 motifs
Use the scale factor of 20 (multiply cm by 20 to get cm on the wall, or multiply cm by 0.2 to get metres on the wall) to complete the table in Step 1.
Worked first row (Motif 1: Dare Valley Pit Wheel):
- Sketchbook size: 6 cm wide × 6 cm high
- Wall width & height in cm (× 20): 6 × 20 = 120 cm wide × 120 cm high
- Wall width & height in m (÷ 100 or × 0.2): 1.2 m wide × 1.2 m high
Slide 4 of 7 · Step 2: Calculate colour zone areas · Art · Year 8
10 minutesStep 2: Work out surface area for the 4 colour zones
The 360 grid squares on the sketchbook design are shared between 4 paint colours. Multiply the number of grid squares in each zone by 0.04 m2 to find the wall area in square metres.
Rule: Wall area (m2) = Number of grid squares × 0.04
Worked first row (Sky & River Teal, 135 squares): 135 × 0.04 = 5.40 m2
Self-check: When you add all 4 wall areas together, they must total exactly 14.40 m2!
Slide 5 of 7 · Step 3: Paint tins & budget calculation · Art · Year 8
12 minutesStep 3: Calculate 750 ml paint tins needed for 2 coats
Outdoor murals need 2 coats of paint so the colours stay bold in Welsh weather. Double each zone’s area for 2 coats, divide by 8 m2 per litre, and work out how many 750 ml (0.75 L) tins to buy.
Shortcut: Since 1 tin (0.75 L) covers 6.0 m2 in one coat, compute:
2-coat area = Wall area × 2 → Exact tins = 2-coat area ÷ 6 → Round UP to whole tins!
Worked first row (Sky & River Teal): 5.40 m2 × 2 = 10.80 m2 (needs 10.80 ÷ 8 = 1.35 L). Tins: 10.80 ÷ 6 = 1.8 tins → round up to 2 tins.
Slide 6 of 7 · Step 4: Scaling guide for the painting team · Art · Year 8
5 minutesStep 4: Write a clear scaling guide for the mural team
Complete Step 4 by writing clear step-by-step instructions explaining how volunteers will chalk the grid onto the wall and transfer the digital overlay without stretching the motifs out of proportion.
- State the chalk grid square size on the wall (20 cm by 20 cm, or 0.2 m by 0.2 m) and how many columns (24) and rows (15) to mark.
- Explain why keeping the same scale factor horizontally and vertically prevents distortion.
- State the final paint order (total tins and cost) and tick the Success Criteria box.
Slide 7 of 7 · Plenary quick check · Art · Year 8
3 minutesQuick check before you hand in your sheet
Check your working against the summary table below before passing your worksheet to the front.
| Item | Correct answer |
|---|---|
| Motif 2 (Viaduct, 12 cm × 4.5 cm) & Motif 3 (Oak, 7.5 cm × 9 cm) | Motif 2: 2.4 m × 0.9 m · Motif 3: 1.5 m × 1.8 m |
| Motif 4 (Book, 10 cm × 2.5 cm) & Motif 5 (Red kite, 3.5 cm × 2 cm) | Motif 4: 2.0 m × 0.5 m · Motif 5: 0.7 m × 0.4 m |
| 4 colour zone areas (1 coat) | Teal 5.40 m2 · Green 4.20 m2 · Gold 3.00 m2 · Charcoal 1.80 m2 (Total 14.40 m2) |
| 750 ml paint tins for 2 coats (at 6 m2 per tin) | Teal 2 · Green 2 · Gold 1 · Charcoal 1 → 6 tins (£84) |