Reading field capacity
Coverage rate answers one question — how long will this job take — but the honest answer depends on efficiency more than on the raw geometry. Two operations with identical width and speed can differ by 30% in real output depending on field shape and how much time goes into turning.
Efficiency by operation type
| Operation | Typical efficiency |
|---|---|
| Large-field broadcast spraying | 85–90% |
| Primary tillage, open field | 80–85% |
| Planting, row crops | 70–80% |
| Combining, average field | 65–75% |
| Small or irregular fields | 55–65% |
Where the time actually goes
- Headland turns. Every pass ends in a turn. Short fields mean proportionally more turning time than long ones.
- Overlap. Avoiding skipped strips means slightly overlapping each pass, which quietly eats a few percent of working width.
- Refilling and unloading. Planters, sprayers and combines all stop to refill or unload. Longer fields mean fewer stops per acre.
- Obstacles. Waterways, power poles and irregular boundaries force slowdowns and extra turns that a rectangular-field formula cannot see.
Three worked examples
A 60 ft boom sprayer at 8 mph, 85% efficiency
(60 × 8) ÷ 8.25 = 58.2 acres/hr theoretical, × 0.85 efficiency = 49.5 acres/hr — about 396 acres in an 8-hour day, typical for large-field spraying where turns are infrequent.
A 15 ft planter at 5 mph, 72% efficiency
(15 × 5) ÷ 8.25 = 9.1 acres/hr theoretical, × 0.72 = 6.55 acres/hr. Planting a 200-acre farm at this rate takes just over 30 hours of actual field time.
A 20 ft brush mower at 6 mph, 65% efficiency
(20 × 6) ÷ 8.25 = 14.5 acres/hr theoretical, × 0.65 = 9.45 acres/hr — the lower efficiency reflects the tighter turning and slower going typical of brush mowing over open-field spraying.
Common mistakes when estimating field time
- Using top speed instead of sustained speed. A tractor rated for 15 mph on the road rarely holds that pulling an implement through soil. Use the speed you actually maintain across a pass, not the gauge's maximum.
- Using frame width instead of working width. A drill's frame might span 20 ft while only 18 ft of it actually plants — the unused edge doesn't count toward coverage.
- Picking one efficiency figure for every field. A 5-acre irregular parcel and a 200-acre rectangle do not turn the same way — use a lower efficiency for the small, awkward fields even with identical equipment.
- Forgetting downtime that isn't "field time." Travel between fields, breakdowns and weather delays don't show up in an acres-per-hour figure at all — pad a multi-day job estimate separately for these.
Clearing new ground before you can work it? The Land Clearing Cost Calculator estimates that job, and the Tree Spacing Calculator helps plan an orchard once the ground is ready.