Find the near limit, far limit and total depth of field from your focal length, aperture, focus distance and sensor size. Shows the hyperfocal distance too.
Depth of field is the zone that looks acceptably sharp. It depends on focal length, aperture, focus distance and the sensor size (through the circle of confusion). Smaller apertures (higher f-numbers), wider lenses and greater distances all increase it.
From the hyperfocal distance H = f squared / (N times c) + f, where f is focal length, N the f-number and c the circle of confusion for the sensor. The near and far limits are then s(H-f)/(H+s-2f) and s(H-f)/(H-s), with s the focus distance.
It is the largest blur spot that still looks sharp in a print, and it scales with sensor size. This tool uses standard values such as 0.029mm for full frame and 0.019mm for APS-C, which is why a smaller sensor shows more depth of field at the same settings.
Use a smaller aperture (a higher f-number), a wider (shorter) focal length, or focus further away. Focusing at the hyperfocal distance gives the maximum possible depth of field for a given lens and aperture.