The official printed US Green Card (Form I-485) photo is 51×51 mm. Use this exact size for printing at home or at a photo kiosk.
Official source: USCIS — Form I-485 Instructions (page 10)
Open the free print tool with this size pre-filled: it lays out 51×51 mm photos on A4, Letter or photo paper at true size in your browser. Nothing is uploaded, no sign-up.
When printing choose “Actual size / 100%”, never “Fit to page”. Home printers scale by 1–2% — use the built-in calibration ruler once.
Get an official-size file with automatic checks (blur, exposure, head height, background). Preview free — pay only when it passes.
The official printed size is 51×51 mm.
At home with the free print tool above (calibrate once with the ruler), or at any photo kiosk with the 51×51 mm size.