Size is not shape
Two numbers describe a print: its size in inches and its shape, the long side divided by the short side. Photos have a shape too. Divide the pixel width by the height: 6,000 × 4,000 gives 1.5, which is 3:2; 4,032 × 3,024 gives 1.33, which is 4:3. The aspect ratio calculator reduces any pair of numbers to its ratio.
When the two shapes differ, a printer that fills the paper has to cut a strip off the photo. The print lab WHCC groups its sizes by ratio for exactly this reason and states that a 2:3 file ordered at a 4:5 size has to be cropped to fit. Orientation does not change the math: a portrait photo on a portrait print loses the same share as a landscape one on a landscape print.
What each print size cuts off
The share of the photo removed, and the side it comes from. "Long side" means the strip comes off the ends of the long edge; "short side" means it comes off the ends of the short edge.
| Print (in) | Ratio | Shape | 3:2 photo loses | 4:3 photo loses |
|---|---|---|---|---|
| 4 × 6 | 3:2 | 1.500 | Nothing | 11.1% of the short side |
| 5 × 7 | 7:5 | 1.400 | 6.7% of the long side | 4.8% of the short side |
| 8 × 10 | 5:4 | 1.250 | 16.7% of the long side | 6.3% of the long side |
| 8.5 × 11 | 22:17 | 1.294 | 13.7% of the long side | 2.9% of the long side |
| 11 × 14 | 14:11 | 1.273 | 15.2% of the long side | 4.5% of the long side |
| 12 × 18 | 3:2 | 1.500 | Nothing | 11.1% of the short side |
| 16 × 20 | 5:4 | 1.250 | 16.7% of the long side | 6.3% of the long side |
| 20 × 30 | 3:2 | 1.500 | Nothing | 11.1% of the short side |
Three patterns stand out. The 3:2 sizes (4 × 6, 12 × 18, 20 × 30) take a 3:2 photo whole and trim 11.1 percent off the short side of a 4:3 one. The 5:4 sizes (8 × 10, 16 × 20) are the squarest and cut the most from a 3:2 photo, 16.7 percent. The in-between sizes, 8.5 × 11 and 11 × 14, are the gentlest compromise for a 4:3 photo, losing only 2.9 and 4.5 percent. A Letter sheet is the same 8.5 × 11 inches as in the paper sizes guide, which matters when you print photos at home.
Square, wallet and panoramic prints
WHCC also lists a 5:7 wallet size (2.5 × 3.5 inches, the same shape as 5 × 7), square prints such as 10 × 10, 16 × 16 and 20 × 20, and 1:2 panoramic prints such as 10 × 20 and 12 × 24. The extreme shapes cost the most:
| Shape | 3:2 photo loses | 4:3 photo loses |
|---|---|---|
| Square, 1:1 | 33.3% of the long side | 25.0% of the long side |
| Panoramic, 2:1 | 25.0% of the short side | 33.3% of the short side |
A square print keeps only the middle of a 3:2 photo, so frame for it when you shoot or pick photos with the subject near the center. A panoramic print works best from a photo that was already wide, or from a crop of a large file that still has enough pixels left.
Two worked examples
A 6,000 × 4,000 photo on an 8 × 10. The short side, 4,000 pixels, maps to the 8 inches. The long side may then only be 4,000 × 10 ÷ 8 = 5,000 pixels, so 1,000 of the 6,000 pixels go, 500 from each end if the crop is centered. That is the 16.7 percent in the table.
A 4,032 × 3,024 photo on a 4 × 6. Now the print is longer than the photo. The long side, 4,032 pixels, maps to the 6 inches, and the short side may only be 4,032 ÷ 1.5 = 2,688 pixels. 336 pixels come off the short side, the top and bottom of a landscape photo.
Pixels needed at 300 and 150 ppi
Multiply each side in inches by the pixels per inch. The PPI vs DPI guide explains the units and what print shops ask for; 300 ppi is the target the shops cited there name. The 150 ppi column, half that density, shows how far a smaller file falls short.
| Print (in) | At 300 ppi | MP | At 150 ppi | MP |
|---|---|---|---|---|
| 4 × 6 | 1,200 × 1,800 | 2.2 | 600 × 900 | 0.5 |
| 5 × 7 | 1,500 × 2,100 | 3.1 | 750 × 1,050 | 0.8 |
| 8 × 10 | 2,400 × 3,000 | 7.2 | 1,200 × 1,500 | 1.8 |
| 8.5 × 11 | 2,550 × 3,300 | 8.4 | 1,275 × 1,650 | 2.1 |
| 11 × 14 | 3,300 × 4,200 | 13.9 | 1,650 × 2,100 | 3.5 |
| 12 × 18 | 3,600 × 5,400 | 19.4 | 1,800 × 2,700 | 4.9 |
| 16 × 20 | 4,800 × 6,000 | 28.8 | 2,400 × 3,000 | 7.2 |
| 20 × 30 | 6,000 × 9,000 | 54.0 | 3,000 × 4,500 | 13.5 |
Resolution left after the crop
Cropping throws pixels away, so the resolution of the print is set by the side that was not cut. These are the pixels per inch that a 6,000 × 4,000 (3:2) and a 4,032 × 3,024 (4:3) photo deliver at each size:
| Print (in) | 3:2, 24 MP | 4:3, 12 MP |
|---|---|---|
| 4 × 6 | 1,000 ppi | 672 ppi |
| 5 × 7 | 800 ppi | 576 ppi |
| 8 × 10 | 500 ppi | 378 ppi |
| 8.5 × 11 | 471 ppi | 356 ppi |
| 11 × 14 | 364 ppi | 275 ppi |
| 12 × 18 | 333 ppi | 224 ppi |
| 16 × 20 | 250 ppi | 189 ppi |
| 20 × 30 | 200 ppi | 134 ppi |
The 12-megapixel photo stays above 300 ppi up to 8.5 × 11 and drops to 275 ppi at 11 × 14 and 189 ppi at 16 × 20. A screen is a different case: the PPI calculator works out the pixel density of a display from its resolution and diagonal.
Fit with borders instead of cropping
The alternative to cutting is fitting: the whole photo goes on the paper and the leftover space stays white. WHCC lists adding a border as one way to handle a ratio mismatch. On a landscape 10 × 8 print, a 3:2 photo that is 10 inches wide is 10 ÷ 1.5 = 6.67 inches tall, which leaves a band of 0.67 inches above and below. That works for a frame with a mat; for a borderless look you crop.
How to crop it yourself
- Pick the print size and look up its ratio in the table: 7:5 for 5 × 7, 5:4 for 8 × 10, 14:11 for 11 × 14.
- Open the photo in the image cropper, set that ratio, and move the frame so nothing important sits in the strip that goes.
- Check the pixels left against the 300 ppi column. If the crop is larger than needed, the image resizer brings it to the exact pixel size, for example 2,400 × 3,000 for 8 × 10.
- Upload the cropped file. A file that already has the print's shape leaves the printer nothing to cut.
If you are not sure which sizes you will order, keep the full original and save one cropped copy per shape: 3:2, 7:5 and 5:4 cover most of the sizes above.
Frequently asked questions
Which print sizes do not crop a photo?
The ones with the same shape as the photo. A 3:2 photo fits 4 × 6, 8 × 12, 12 × 18 and 20 × 30 exactly. None of the common sizes in the table is 4:3, so a 4:3 photo always loses a little, least at 8.5 × 11 and 11 × 14.
How much of my photo is cut off on an 8 × 10?
An 8 × 10 is 5:4, much squarer than most photos. A 3:2 photo loses 16.7 percent of its long side, about a twelfth from each end. A 4:3 photo loses 6.3 percent of its long side.
Why does my 5 × 7 print cut off heads?
A 5 × 7 is 7:5, so a 3:2 photo loses 6.7 percent of its long side. If the subject is close to the top or bottom edge of a portrait photo, that strip is where heads and feet sit. Crop the photo yourself to 5:7 before ordering and you choose which strip goes.
How many pixels do I need for an 8 × 10 print?
At 300 pixels per inch, 2,400 × 3,000 pixels, which is 7.2 megapixels. At 150 pixels per inch, half that density, it is 1,200 × 1,500. Multiply each side in inches by the pixels per inch you want.
Can I print a photo without cropping it?
Yes, by fitting it inside the print with white bands instead of filling the paper. The print lab WHCC names adding a border as one of the ways to handle a file whose ratio does not match the print. On an 8 × 10 a 3:2 photo then fills 10 × 6.67 inches with two bands of about two thirds of an inch.