What the calculator actually estimates
Working width times ground speed gives a theoretical area rate, but no mower or sprayer covers its full width — adjacent passes overlap. The calculator multiplies width by speed and shaves off the overlap to produce an effective area-per-hour figure. Divide your plot by that rate to get a finish time.
Treat the number as a budget, not a schedule. Real fields have headland turns, refuel stops and the occasional fence post; padding the result by 15–25% gets you closer to wall-clock time.
The two formulas
Both equations are unit-agnostic — feed them consistent units (e.g. metres and m/s, or feet and ft/s) and you'll get sensible output.
area_per_hour = width × speed × (1 − overlap)
time = area / area_per_hour
width— Effective working width of the implementspeed— Sustained forward speed during a passoverlap— Fraction of the working width that overlaps the previous pass (10% = 0.10)area— Total plot area to coverarea_per_hour— Effective area rate after the overlap deduction
Getting an estimate that matches reality
The arithmetic is straightforward; the failure mode is feeding it the catalogue speed rather than the speed you'll actually hold across the plot.
- Use sustained speed, not maximum speed — Knock 15–25% off the spec-sheet figure for anything but billiard-flat ground. Sloping or stony fields cost more than most operators expect.
- Pad the overlap honestly — A 10% default is sensible for mowing or tillage. Anything with boom sway or where missed strips cost money (spraying, fertiliser spreading) justifies 15–20%.
- Add turn time for small fields — Headland turns aren't in the formula. On a 2-acre paddock with a 12-ft implement they can add 20–30% to the total; on a quarter-section they vanish into the rounding.