Match width and height scale
If the width scale is 2x but the height scale is 1.8x, crop the reference or change the target size before drawing the grid.
Free drawing grid calculator
Grid size calculator for drawing
Enter reference size, target drawing size, rows, and columns to get the scale factor and cell sizes. Then open the same grid on your photo.
Scale and cell planning
Match your reference to the final drawing
Reference image
Target drawing
Measure from one edge
On paper, canvas, or a wall, mark every grid line from the same fixed edge so tiny ruler errors do not accumulate.
Keep the same cell count
The reference and target must use the same rows and columns. The cells can get larger, but the coordinates should not change.