300 DPI is for close, detailed viewing. 150 DPI doubles print size for the same pixels and often looks fine from farther away.
What stays the same
Your file’s pixel count does not change when you pick a different DPI target. You either print larger with lower density or smaller with higher density.
Practical takeaway
Choose DPI based on viewing distance and criticality of detail — then check whether your pixels support that print size.
FAQ
Which should I use for print planning?
Use pixels and target print size. Treat DPI/PPI as the density you want on paper, not as a magic quality switch.