You are standing in front of a wall. You know the size you want. You do not know if the print will hold together at that size, or if you will see the dots.
The fear is reasonable. A file that looks sharp on a screen can fall apart at 40 inches, and most galleries will not tell you the source resolution until after you have paid.
Here is how to know before you buy.
The Number That Matters Is PPI, Not DPI
PPI means pixels per inch — how many pixels from the original file land in each inch of the printed surface. DPI means dots per ink, which is the printer’s business, not yours. A 300 PPI file can be printed at 1440 DPI or 2880 DPI; the printer is working harder, but you are not getting more detail.
What you need to know is the PPI of the file at the size you are buying. If the seller does not publish it, the file is probably being stretched.
The Old Rule Is 300 PPI. The Real Rule Depends on How Far You Stand.
A print you inspect at arm’s length — about two feet — wants 300 PPI or very close to it. At that distance, the human eye resolves about 300 distinct points per inch. Go below 200 PPI and you will see softness. Go below 150 PPI and you will see the grid.
But a print you hang above a sofa and view from six feet away can drop to 150 PPI and still read as sharp. A print you hang in a stairwell and view from ten feet away can drop to 100 PPI. The formula is simple: divide the viewing distance in inches by two. That is your minimum PPI.
Viewing distance 24 inches: you need 300 PPI. Viewing distance 72 inches: you need 150 PPI. Viewing distance 120 inches: you need 100 PPI.
How to Calculate PPI From the Size You Want
If the seller gives you the source file dimensions in pixels, the math is one line. Take the pixel width, divide by the print width in inches. That is your PPI.
Example: a file is 7200 pixels wide. You want a 24-inch print. 7200 divided by 24 is 300 PPI. That print will be sharp at arm’s length.
Same file, 36-inch print: 7200 divided by 36 is 200 PPI. Still acceptable at arm’s length, and perfectly sharp from six feet.
Same file, 48-inch print: 7200 divided by 48 is 150 PPI. Now you are in the zone where it looks sharp from the sofa but soft up close. If this is going above a console table where someone will stand near it, that softness will bother you.
What Happens When PPI Drops Below Your Threshold
At 200 PPI, edges lose crispness. Fine lines thicken slightly. Text becomes harder to read. Faces lose the sharpness around the eyes and mouth.
At 150 PPI, the image reads as an image, but detail is visibly lost. If the work has fine texture — brushstrokes, fabric, intricate line work — it will blur.
At 100 PPI, you see the pixel grid if you step close. From across the room it may still work, but the contract between you and the print has changed. You are no longer looking at detail. You are looking at shape and colour.
Below 100 PPI, the print is decorative, not detailed. It belongs on a wall you pass, not a wall you study.
How to Get the Number Before You Buy
Ask for the source file resolution in pixels, and do the math yourself. If the seller will not give it, assume the file is being stretched and the PPI is below 200.
At Printasso, every work is AI-generated at a minimum of 300 PPI for the largest size offered, and the math is the same across poster, canvas and framed. A 24×36 inch print has the same pixel density as an 18×24 inch print from the same file, because the file was built for the largest size first. You are not stretching a smaller file; you are cropping a larger one.
What About Canvas vs Poster Paper?
Canvas has texture. The weave of the fabric breaks up the pixel grid slightly, so a canvas print at 200 PPI can look as sharp as a poster at 250 PPI. The tradeoff is that fine detail — small text, thin lines — gets lost in the weave.
Poster paper is smooth matte with no texture, so the pixel grid is more visible if the PPI is low, but fine detail survives. If the work has intricate line work or small type, paper is the honest choice.
The Real Test: Arm’s Length
When the print arrives, stand at arm’s length. If you see softness, step back to where you will actually view it. If it sharpens, the PPI is fine. If it does not, the file was stretched and you should have asked for the number.
Printasso prints ship flat, unframed, and free within the continental United States. The PPI is built in. The only variable is the wall.
More from Ruby: Ruby’s writing. Prints ship free within the continental US.