Pixels needed, worked through
Print resolution is dots per inch, so the pixel requirement is just the print size in inches multiplied by the dpi in each direction. At the lab standard of 300 dpi:
| Pixels at 300 dpi | Megapixels | |
|---|---|---|
| 4 x 6 in | 1200 x 1800 | 2.2 |
| 5 x 7 in | 1500 x 2100 | 3.2 |
| 8 x 10 in | 2400 x 3000 | 7.2 |
| 11 x 14 in | 3300 x 4200 | 13.9 |
| 16 x 20 in | 4800 x 6000 | 28.8 |
A 12-megapixel phone camera produces roughly 4032 by 3024 pixels, which covers a 4 by 6 with pixels to spare and covers an 8 by 10 at about 302 dpi on the short side. It falls short of a 16 by 20 at 300 dpi by a wide margin, reaching about 190 dpi, which is a perfectly reasonable print for a wall but not a 300 dpi one.
Note that these are the minimums for printing the whole frame without cropping. Crop into the image and the requirement rises in proportion: use half the frame and you need twice the linear resolution to keep the same dpi.
Upscaling does not add detail
This is the single most useful thing to understand about print resolution. If a file is 1500 pixels across and the print needs 2400, resizing it to 2400 does not recover anything. Resampling algorithms interpolate — they invent intermediate pixels from the neighbours they already have. Bicubic interpolation produces a smooth result that looks soft. Modern machine-learning upscalers produce a sharp result that looks convincing, but the fine texture they add is a plausible invention rather than a record of what was in front of the lens. On a landscape it usually passes; on a face or on text it can be obvious and unpleasant.
Changing the dpi field in an image file's metadata does nothing at all. That number is a note attached to the file saying what physical size the pixels are intended to occupy. Setting a 1500 pixel image from 72 dpi to 300 dpi does not change a single pixel; it changes the intended print size from 20.8 inches to 5 inches. What determines print quality is the pixel count and nothing else.
When a file is short, the honest options are to print smaller, to print at a lower dpi because the piece will be viewed from further away, or to accept softness. A print held at arm's length is being viewed from roughly 14 inches and wants 250 to 300 dpi. A framed print on a wall looked at from six feet is entirely convincing at 120 to 150, which is why billboards get away with under 20.
Why 4:3 does not fit a 4 by 6
A 4 by 6 print is a 3:2 rectangle, 1.5 to 1. Most phone cameras save 4:3, which is 1.333 to 1. Those do not match, so filling the sheet requires losing something.
The arithmetic: the shorter ratio divided by the longer gives 1.333 divided by 1.5, which is 0.889, so 11.1 percent of the long dimension goes. With a centred crop that is 5.6 percent off the top and 5.6 percent off the bottom. In a portrait it takes the space above the head; in a group shot lined up along the frame edge, it takes whatever was nearest the border.
| Source | 4 x 6 (1.5) | 5 x 7 (1.4) | 8 x 10 (1.25) | 16 x 20 (1.25) |
|---|---|---|---|---|
| 4:3 phone (1.333) | 11.1% off top/bottom | 4.8% off top/bottom | 6.3% off the sides | 6.3% off the sides |
| 3:2 camera (1.5) | exact | 6.7% off the sides | 16.7% off the sides | 16.7% off the sides |
| 1:1 square | 33.3% off the sides | 28.6% | 20.0% | 20.0% |
| 16:9 (1.778) | 15.6% off top/bottom | 21.3% | 29.7% | 29.7% |
Three ways to deal with it. Order with white borders, so the whole frame prints and two edges carry a band. Crop the file yourself before ordering, which is the only method where you decide what goes rather than the lab's centred default. Or set the camera to shoot 3:2 in the first place, which most phones offer, and stop having the problem for 4 by 6 prints. The 8 by 10 is a 5:4 sheet and is closer to a 4:3 source than to a 3:2 one, which surprises people who assume the larger sizes follow the same shape.
Sizes and what they cost
The US retail set runs 4 by 6, 5 by 7, 8 by 10, 11 by 14 and 16 by 20. Only the first is a 3:2 rectangle. The 5 by 7 is 7:5, the 8 by 10 and 16 by 20 are both 5:4, and the 11 by 14 is 14:11. That inconsistency is historical rather than designed, and it means changing size usually changes the crop as well.
Cost rises far faster than area. A hundred 4 by 6 prints is a small amount of money; the same hundred at 8 by 10 is roughly ten times that, and at 16 by 20 it becomes a serious purchase. This is why almost every real order is mostly 4 by 6 with a handful of enlargements, and why framing rather than printing is usually the larger line item once you pass 8 by 10.
Free shipping thresholds
An order sitting at 28 dollars against a 35 dollar free shipping threshold invites adding prints to save 5 dollars of shipping. Spending 7 to save 5 is only sensible if the extra prints were wanted anyway. The calculator shows the gap and roughly how many prints would close it, so the comparison is visible rather than assumed. Store pickup, where the lab offers it, removes the question — set shipping to zero.
Elsewhere on the site
Physical paper dimensions, printable area after margins and the Letter against A4 problem live in the paper size calculator. For pure ratio arithmetic on pixel dimensions, with no print or cost involved, use the aspect ratio calculator, and image crop ratio lets you crop a file to a chosen shape in the browser. Screen pixel density, which is the same division applied to a display rather than a sheet of paper, is the PPI calculator. To read the actual dimensions out of a file you already have, image info reports them without uploading anything.
Questions people ask
How many pixels do I need for a 4 by 6 print?
1200 by 1800 at 300 dpi, which is 2.2 megapixels — less than any phone made in the last fifteen years produces. That figure assumes you print the whole frame. A 4:3 phone photo has to lose 11.1 percent of its height to fill a 4 by 6, so the pixels doing the work are fewer than the file contains. At the low end, 4 by 6 prints from a 200 dpi source (800 by 1200) still look fine held in the hand; below about 150 dpi the softness starts to show on edges and text within the picture.
What happens if my photo has fewer pixels than the print needs?
You choose between size and sharpness. Printing it anyway at a lower effective dpi is usually the right answer — the calculator shows what dpi you would actually be printing at, and anything from 200 up is hard to fault by eye at normal viewing distance. Upscaling the file first does not add information; interpolation invents pixels from the neighbours, and AI upscalers invent convincing texture that was never recorded. On landscapes it passes, on faces and on any text in the image it often looks wrong. The third option is to print smaller, which the calculator gives as the largest size your file supports at your chosen dpi.
Why do my phone photos get cut off when printed?
The shapes do not match. Phones default to 4:3, which is 1.333 to 1, and a 4 by 6 print is 3:2, which is 1.5 to 1. To fill the sheet the lab crops 11.1 percent off the long dimension, normally centred, so 5.6 percent goes from the top and 5.6 percent from the bottom. Order with white borders to keep everything, crop the file yourself to decide what goes, or switch the camera to 3:2 so future photos match. An 8 by 10 is a different shape again, 5:4, so the same photo loses 6.3 percent off the sides instead.
Is 300 dpi always necessary?
No. Three hundred is the lab default because it exceeds what the eye resolves at reading distance, roughly 14 inches, with margin to spare. Viewing distance is the variable everyone forgets. A print you hold wants 250 to 300. A framed 16 by 20 seen from six feet is convincing at 120 to 150, which is why a 12-megapixel phone file that reaches only about 190 dpi at that size still produces a print people are happy with. Set the target dpi in the calculator to match how the print will actually be looked at rather than to a number you read somewhere.
Are the reference prices accurate for my lab?
They are a rough middle of US retail and should be treated as orientation only. Online labs running first-order promotions, warehouse clubs, drugstore kiosks and professional print houses can differ by a factor of five on the same size, and volume breaks at 100, 300 and 500 prints are common but not universal. Untick the reference box and enter what your lab quotes. The part that holds regardless of vendor is the relative shape: each step up in print size costs roughly two to three times the one below, and past 8 by 10 the frame usually costs more than the print inside it.