PencilCADDrawing 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. Here’s the method, and how to do it with Apple Pencil.
1. Pick a scale
Decide what one grid square stands for before you draw anything, and write it on the page. Choose a scale that fits the largest size on one page with room to spare for dimensions.
- Small parts and 3D prints: 1 square = 1 mm, 5 mm or 10 mm.
- Furniture and woodworking: 1 square = 1 inch or 2 inches.
- Rooms and gardens: 1 square = 1 foot, or 1 square = 0.5 m.
Keep it round. One square for 10 mm is easy to count. One square for 7 mm isn’t.
2. Count squares, don’t eyeball
Divide each real size by the scale and draw that many squares. A 480 mm shelf at 1 square = 20 mm is 24 squares. When a size doesn’t land on a whole square, round the drawing and keep the exact number in the dimension: the sketch shows the shape, the number is what you build to.
3. Work out slanted lines from their run and rise
Horizontal and vertical lines count directly. A slanted line doesn’t, so place its two ends by counting across and up, then join them. If you need its length, it’s the square root of run² + rise². In the figure, the corner cut runs 3 squares across and drops 4, so it’s exactly 5 squares long: 50 mm at this scale.
4. On isometric paper, count along the axes
The same idea works in 3D. Count lattice steps along the three isometric directions: height, width and depth. Lines that don’t follow one of those directions aren’t shown at true length, so place their ends by counting along the axes, as with slanted lines on square grid.
5. Write the sizes on it
A to-scale sketch still needs its numbers. Scaled lines are for proportion. Dimensions are for building. Put the overall sizes on first, then the features, and note the scale and units once in a corner.
To-scale sketches in PencilCAD
PencilCAD keeps your lines on the grid, so counting squares is exact, and labels every dimension with the length it stands for.
- Open More and choose Grid, Dot grid or Isometric paper. Pick Small, Medium or Large to set how many squares fit on a page.
- In Settings → Tools, choose CAD. Tap Measure, tap it again, and set what one square stands for, such as 1 square = 10 mm.
- Draw with the Line tool. With Snap to grid on, every line starts and ends on a grid point, so each length is a whole number of squares.
- For rectangles, use Shape. Its corners snap to the grid too.
- Drag out dimensions with Measure. Each is labelled with its real length at your scale, and a PDF export prints the page at a true scale.