Proportion & Grid-Transfer Calculator
Enter your reference size, the grid you drew on it, and your target size — get the scale factor, the matching target cell size, and a check for stretching before you start drawing.
Scaled grid
Keeping proportions honest
The grid-transfer method has been a studio staple for centuries because it turns a hard problem — copying complex shapes at a new size — into a series of small, easy comparisons. The only way it goes wrong is when the width and height don't scale by the same factor, which squashes circles into ovals and throws off every angle in the drawing.
This calculator does the ratio arithmetic for you: one scale factor, applied consistently to width, height, and every grid cell, plus an optional check against the height you're actually planning to use.
Frequently Asked Questions
What is the grid-transfer method?
It's a proportion-drawing technique: draw an evenly spaced grid over a reference photo, draw a grid with the same number of rows and columns (but a different cell size) on your final surface, then copy what's in each small reference square into its matching larger square. Because every square is scaled by the same factor, the whole image enlarges without distortion.
How do I find the right scale factor?
Divide your target width by your reference width — that single number is the scale factor for every other measurement in the drawing, including each grid cell. If your reference is 1000 units wide and your final surface is 4000 units wide, everything scales up by exactly 4×.
Why does the tool warn me about distortion?
If you scale the width by one factor but plan a final height that doesn't match that same factor applied to the reference height, the image will look stretched or squashed. Entering your planned final height lets the tool compare it against the proportionally correct height and flag a mismatch bigger than about 2%.
Does the grid have to be square cells?
No — this method works with any consistent grid, but square cells are the easiest to judge by eye, since a shape that looks off inside one square is usually easy to spot and correct before it's copied at the larger size.
Educational tool only. Enter both dimensions in the same unit (inches, centimetres, pixels) for the scale factor to be meaningful.