Reference-to-Paper Fit Calculator
Find the largest size you can draw a reference at on a given paper size while keeping its proportions intact.
Units are whatever you entered, inches, cm, or reference pixels all work as long as reference and paper use the same one. Leave room in that margin for tape and for your hand.
How it works
Enter your reference's width and height (any unit, inches, centimeters, or the pixel dimensions of a photo all work, since only the ratio between them matters), then pick a paper size. The calculator finds the scale that makes the reference as large as possible without running off either edge of the paper, keeping the original proportions intact, and tells you the finished drawing size plus how much margin is left over.
Worked example: an 8 in by 10 in reference on 11 in by 14 in paper. Scaling to fit the width would give 1.375x (11 divided by 8), and scaling to fit the height would give 1.4x (14 divided by 10). The calculator takes the smaller of the two, 1.38x, so the drawing comes out 11 in wide and 13.75 in tall, using up the full width and leaving a small margin at the bottom. If it had used the height-based scale instead, the drawing would have been too wide for the paper.
FAQ
Why does it use the smaller of the two possible scales?
Because the larger scale would overflow one edge of the paper. Using the smaller of the width-fit and height-fit scales is what guarantees the whole reference lands inside the sheet, with the leftover space showing up as margin on whichever dimension wasn't the limiting one.
My reference is a photo. Does resolution matter here?
Only the width-to-height ratio matters for this calculator, not the pixel count. A phone photo at 3024 by 4032 pixels has the same proportions as a 3 in by 4 in print, so you can plug in either the pixel dimensions or a physical size and get the same scale factor back.
Should I crop my reference before or after using this calculator?
Before. Cropping changes the width-to-height ratio, which changes the scale and the final drawing size. Decide on your composition and crop first, then run the numbers on the cropped dimensions so the fit is accurate.
What if I want extra margin on purpose, for a mat or frame?
Enter a slightly smaller paper size than what you actually have. If your paper is 11 in by 14 in but you want a 1 in border all around, run the calculator at 9 in by 12 in instead and center the result on the full sheet.
For more on working from photos and choosing paper, see how to draw from reference photos, how to choose your first sketchbook, and the best paper for pencil drawing and sketching.