Lab print specs explained: what the labs actually publish
Every photo lab publishes (or buries) a spec page telling you what it wants: how many pixels, which file formats, what colour space. We fetched the official pages of four labs — mPix, Nations Photo Lab, WHCC and Snapfish — and transcribed what they say, verbatim where it matters. One honest finding up front: the labs do not agree with each other, which is itself the most useful fact on this page.
Key takeaways
- mPix's chart: optimum at 250 PPI, minimum at 100 PPI for every size; JPEG/PNG, RGB only.
- Nations Photo Lab: three columns — 125 / 180 / 300 PPI; "125 PPI or higher… print beautifully".
- WHCC: files "as close to the desired print size as possible when it's at 300ppi"; relabelling adds no quality.
- Snapfish publishes no numbers — it warns in-software when a file is too small for a chosen product.
- One lab's "too small" is another lab's "optimal": check your lab's page before resizing anything.
mPix: the 250 / 100 chart
mPix's help article "Requirements to upload your photos" carries a full chart with optimal and minimum pixel dimensions for every product. The pattern is exact: optimum = inches × 250, minimum = inches × 100. A 4×6 wants 1000 × 1500 optimal or 400 × 600 minimum; an 8×10 wants 2000 × 2500 or 800 × 1000; a 24×36 wants 6000 × 9000 or 2400 × 3600. Files: "Digital pictures are accepted in JPEG and PNG formats. We are able to print from RGB files only." Below the chart minimum, mPix's ordering software flags the image, and the company invites customers to email a file for a quality check before ordering — a service worth knowing about for borderline files.
Nations Photo Lab: the 125 / 180 / 300 ladder
Nations' "Image Resolution Guidelines" page builds its chart on three PPI columns — 125, 180 and 300 — for dozens of sizes (4×6: 500 × 750 / 720 × 1080 / 1200 × 1800; 24×36: 3000 × 4500 / 4320 × 6480 / 7200 × 10800). The framing is unusually candid: printers are calibrated so "high resolution images (125 PPI or higher) print beautifully", and the guide repeats the honest physics that "resolution (pixels) cannot be added to an image once it is captured by enlarging the image, it can only be removed." For files below the line it suggests printing smaller, choosing textured products (canvas, linen), or displaying at a greater viewing distance — the same distance logic as viewing distance & DPI.
WHCC: 300 ppi, said plainly
White House Custom Colour's file-prep help is the most direct of the four: "the original file needs to be as close to the desired print size as possible when it's at 300ppi." Its method section is a mini-tutorial in the PPI/DPI distinction (explained here): uncheck "Resample", type 300 ppi, and read off the largest size your pixels truly support. The page is equally blunt about the trap: converting an 8×10 file from 72 ppi to 300 ppi "will not add any quality to the file, the appearance will be the same." For judging enlargements, WHCC recommends printing a crop at final size and judging it "from an average viewing distance" — distance again, in the lab's own words.
Snapfish: warnings instead of numbers
Snapfish's support article "Understanding how image resolution affects print quality" stays qualitative: resolution is "the amount of detail an image holds… measured in pixels per inch"; higher is better; the uploader shows a warning triangle when a file is too small for the chosen product. Its practical advice: upload at "full resolution" rather than "standard resolution" for "larger items, like posters, canvases, and photo panels". No PPI table exists on the page we fetched — so any specific Snapfish numbers you see on third-party cheat sheets did not come from Snapfish. (We checked Shutterfly's help centre too; its spec pages would not load for verification, so this article quotes none of its numbers — verify-or-drop.)
Side by side
| mPix | Nations | WHCC | Snapfish | |
|---|---|---|---|---|
| Optimal guidance | 250 PPI chart column | 300 PPI chart column | "as close as possible… at 300ppi" | Not published (upload full resolution) |
| Stated minimum | 100 PPI chart column | 125 PPI ("or higher… print beautifully") | Not a hard number; test-and-judge guidance | Not published (in-app warning) |
| Formats | JPEG, PNG; RGB only | Per product pages | Per product pages | Per product pages |
| Low-file advice | Software warning; email for a check | Print smaller / textured product / more distance | Crop-test at final size, judge at average distance | Re-upload at full resolution |
All four pages fetched and verified 2026-11-16: mpix.com/help/uploading-photos · nationsphotolab.com/pages/guide-image-resolution · whcc.com/help/file-prep/image-resolution · support.snapfish.com. Specs change — always re-check before a big order.
How to use the disagreement
Treat the spread as a map, not a conflict. mPix's 250-optimal tells you where diminishing returns begin for continuous-tone photo paper; WHCC's 300 reflects the conservative default most file-prep advice standardized on (its origin story: where 300 PPI comes from); Nations' 125 floor shows how low calibrated photo printers can go before a lab bothers to warn you. For any specific order, run your pixels through the DPI calculator, read the verdict band against the quality ladder, and then open your actual lab's page — its chart is the only one that gates your order.
Photo-print service (concept pick)
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PrintDPI has no relationship with any lab named on this page. Labs are cited because they publish their specs publicly; names are trademarks of their owners.