Choose a test object. Use a round object with a diameter between 80mm and 90mm — a bottle, tumbler, or pipe offcut works well. Measure the exact diameter with calipers and note it down.

Place it on the flat bed. Support it with a V-block or two parallel pieces of material so it cannot roll. Focus the lens on the very top of the object.

Engrave a series of test rectangles. In your laser software, create a row of filled rectangles, each one 2mm wider than the last — start at 10mm wide and go up in 2mm steps: 10, 12, 14, 16, 18, 20mm and so on. Keep them short (10–15mm tall) and use your normal engraving settings. Engrave them all in one job, centred on top of the object.

Find the widest one that still looks sharp. Inspect each rectangle. The narrow ones will look crisp and clean. As the width increases, the outer edges will start to look softer or lighter as they move out of focus. Find the last rectangle where the quality is still acceptable.

Enter the values below. Enter your test object’s diameter and the artwork width of the widest rectangle that still looked good — use the width value from your design, not a measurement taken from the engraved result. The reverse calculator will determine your depth of field and apply it to the main calculator above.