Print size and DPI

DPI is not a quality score stored in the universe. It is pixels divided by the inches you intend to print. A 1200-pixel-wide file at 300 DPI is 4 inches wide. The same file at 150 DPI is 8 inches wide and looks softer.

Upscaling doubles the pixels, so it doubles the inches you can claim at the same DPI. The new pixels are interpolated. Stand where the print will be seen. A poster across a room tolerates a lower DPI than a photo in the hand.

Use the calculator, then upscale only if the inches are short of the frame you bought.