Resolution here means pixels, not a DPI stamp in the file header
People mix up three numbers: pixel width, pixel height, and dots-per-inch in EXIF. Portals almost always check pixels. A “300 DPI” JPEG that is 800 px wide is still 800 samples across — printing it at 300 DPI yields a 2.7-inch print, not a poster. Use this page when the brief is a number: minimum width, square listing, or “at least 1500 on the short side.” Progressive 2× Canvas steps usually look cleaner than one 4× leap because each interpolation is smaller. Optional sharpen, contrast, and brightness can hide some softness; they cannot reconstruct a license plate that was 12 px tall. Cap is 10,000 per side. Native JPG/PNG/WebP; convert HEIC first. If the destination actually wants a smaller file, stop — that is Image Resizer, not this spoke. If they want print inches, open the printing spoke and multiply inches by 150 or 300. Growing pixels helps when you are 10–40% short of a floor. It hurts when you are 4× short: the result meets the checkbox and still looks mushy in a zoom viewer. Screenshot-of-a-screenshot sources are the worst case: you are interpolating compression blocks. Go back to the camera roll or the designer’s export when that file still exists.