Calculate the required pixel dimensions
Use pixels = inches × pixels per inch. At 300 pixels per inch, a 12 × 24 inch sheet needs 3600 × 7200 pixels; a 12 × 48 inch sheet needs 3600 × 14400 pixels. At 150 pixels per inch those counts are halved in each direction. Choose the resolution for your production requirements, not just because a number is available in an export menu.
Large sheets consume memory as well as storage. A 3600 × 14400 RGBA bitmap alone contains about 207 MB of raw pixel data before temporary processing buffers. Its compressed download may be much smaller. Preview zoom does not change the required exported pixels.
Inspect the file without resampling
- Open the exported PNG in the receiving application.
- Inspect its pixel width and height first.
- Check the print resolution and displayed dimensions in inches or millimeters.
- When checking existing pixels in Photoshop, disable Resample before changing how resolution is interpreted.
- Print a measured test at actual size rather than allowing the printer dialog to fit the sheet automatically.
A destination program may interpret missing or changed resolution metadata differently. Changing the interpretation without resampling does not create new image detail. Resampling changes the pixel data and can conceal a size problem by generating a different bitmap. Keep the original export while investigating.
Treat transparency separately from size
PNG can retain transparent areas, while an opaque white or black background is part of the pixels when it has been flattened into the artwork. A dark preview behind transparent pixels does not prove that the file contains a black background. Check it over a light and a dark background or use the destination application’s transparency grid.
Registration ink is also part of a marked print file. Do not confuse preview safe-area guides with intended printed marks. Inspect the exported file itself; a clean preview is not sufficient evidence that guide lines have been excluded.
Keep base artwork and marked print files distinct
A base image and an expanded marked print can have different page dimensions while retaining the same artwork scale. Adding space around the base should not stretch the design. Label and retain both outputs, and compare one known feature between them before sending a production job.
In Auto Arrange for Print, check the selected paper size, export resolution and output type together. Confirm registration placement against your cutter workflow. Neither the file extension nor a successful download establishes that a particular machine will read its marks correctly.