Grid maker › Scaling to your paper

Enlarging a photo onto your paper

A grid is a scaling device first and a copying aid second. Get the proportions and the arithmetic right and the enlargement almost draws itself.

The grid method's real job is not copying — it is scaling. A 15cm photo becomes a 50cm drawing, or a two-metre mural, without a projector and without guessing. The whole trick is that the number of cells stays the same while the size of each cell changes.

The one rule that matters

Same number of rows and columns on both surfaces. Not the same cell size — the same count. If your gridded reference is 20 columns wide, your paper is 20 columns wide, whether those columns are 8mm or 8cm.

Working out your cell size

Measure the width of your drawing area and divide by the number of columns.

• A 30cm wide sheet with 20 columns gives 15mm squares
• A 40cm canvas with 16 columns gives 25mm squares
• A 2m wall with 10 columns gives 20cm squares
• A 56 × 71cm chart paper sheet with 14 columns gives 4cm squares
• A half-imperial sheet, 38 × 56cm, with 19 columns gives 2cm squares

Mark that spacing along the top and bottom edges, join the marks, then do the rows the same way. If the division lands on an ugly number, change the column count — the grid is there to serve you.

Matching the shape of the paper

This is where enlargements usually go wrong. A 3:2 photograph will not fill a square sheet, and forcing it stretches every face in the picture. You have three honest options:

1. Crop the reference to the shape of your paper before you grid it. In the grid maker, choose your sheet format and then zoom and drag the photo until it fills the page the way you want.
2. Leave a margin. Rule the grid inside a rectangle that matches the photo's proportions and accept white space around it.
3. Change the paper. Trim the sheet to the photo's ratio.

What you should not do is stretch the grid to fit. Rectangular cells on one side and square cells on the other is exactly the error that produces drawings where something is subtly wrong and nobody can say what.

Printing at true size

If you want the printed reference itself to be a specific size, choose a sheet format in the grid maker — A4, A3, A5, Letter, Legal or a custom size in millimetres. The download is generated at those exact physical dimensions, and the readout under the canvas tells you how many millimetres each square measures.

Then print at 100%, not "fit to page". Fit-to-page silently rescales by a few percent to respect printer margins, which is enough to make the millimetre figures wrong. Most print dialogs call the setting Actual size, 100%, or Custom scale: 100.

Printing bigger than your printer

For A3 or larger output from an A4 printer, either use the tiling or "poster" option in your print dialog, or take the PNG to a copy shop. Export at 2× or 4× first so the lines stay crisp at the larger size.

Very large work: transfer in stages

For murals and big canvases, one grid rarely does the job. A two-pass approach is far more forgiving:

1. Grid the reference at about 8 columns and chalk the same grid on the wall. Block in the large masses — where the figure sits, where the horizon runs.
2. Re-grid a single region of the reference at 16 columns and use it to refine the part that needs precision, like a face or lettering.

Snap a chalk line for the wall grid rather than measuring each line individually, and check your diagonals: on a correctly ruled rectangle, the two corner-to-corner diagonals are equal. If they are not, your grid is a parallelogram and everything drawn in it will lean.

Canvas and toned surfaces

On canvas, rule the grid with thinned paint or a light charcoal line rather than graphite — pencil can resist paint and show through thin layers. On toned or dark paper, set the grid maker's line colour to white so your printed reference reads the same way as your surface.