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Drawing to scale on iPad

A to-scale sketch doesn’t need CAD. It needs a scale you decide up front, paper with a grid to count on, and lines that stay on that grid.

1. Pick a scale

Small parts, 3D prints 1 square = 1, 5 or 10 mm Furniture, woodworking 1 square = 1″ or 2″ Rooms, gardens 1 square = 1 ft or 0.5 m
Fit the biggest size on one page, with room for dimensions.

Decide what one square stands for, and write it on the page. Keep it round: 10 mm counts easily, 7 mm doesn’t.

2. Count squares, don’t eyeball

1 square = 20 mm 4 8 12 16 20 24 480 mm 24 squares × 20 mm
480 mm ÷ 20 mm = 24 squares.

Divide each size by the scale and draw that many squares. Round the drawing, never the dimension.

3. Work out slanted lines from their run and rise

80 50 30 40 50 1 square = 10 mm √(3² + 4²) = 5 squares
3 across, 4 down: 5 squares, 50 mm.

Count a slanted line’s ends across and up, then join them. Its length is √(run² + rise²).

4. On isometric paper, count along the axes

4 wide 3 deep 2 high brace: not true length
Count along the three axes.

Count lattice steps along height, width and depth. Off-axis lines aren’t true length, so count their ends.

5. Write the sizes on it

90 40 50 2× Ø10 1 square = 10 mm
Overall, then features, then the scale.

Scaled lines show proportion; dimensions are what you build to. Note the scale and units once, in a corner.

To-scale sketches in PencilCAD

Grid Dot grid Isometric
More: pick the paper
Units 1 SQUARE = 10 mm Set scale
Tap the units chip
30 mm
Line snaps to grid points
Scale 1:1 25 mm
PDF at true scale
  1. Open More and choose Grid, Dot grid or Isometric paper, Small, Medium or Large.
  2. Tap the toolset chip beside the page count and choose CAD, or use Settings → Tools. Tap the units chip at the top right and set 1 square = 10 mm.
  3. Draw with Line, Rectangle or Circle. With Snap to grid on, every end lands on a grid point.
  4. Drag out dimensions with Dimension: each reads its real length, and a PDF prints at true scale.

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