Case 1
- Working width
- 5ft
- Ground speed
- 5mph
- Field efficiency
- 80%
2.4ac/h
Open with these valuesAcres Per Hour Calculator
2.4acres/hour
Result: 2.4 acres/hourAcres per hour is width in feet times speed in mph times efficiency, divided by 825. A 5-foot deck at 5 mph and 80% efficiency covers 2.4 acres per hour, so one acre takes about 25 minutes. The 8.25 in the formula is 43,560 square feet per acre divided by 5,280 feet per mile.
The numbers at a glance
Held fixed: Working width 5.0 ft, Ground speed 5.0 mph.
| Field efficiency (%) | Result (ac/h) |
|---|---|
| 60 | 1.8 |
| 70 | 2.1 |
| 80Your value | 2.4 |
| 90 | 2.7 |
| 100 | 3.0 |
Worked examples
Case 2
- Working width
- 14ft
- Ground speed
- 7mph
- Field efficiency
- 80%
9.5ac/h
Open with these valuesCase 3
- Working width
- 40ft
- Ground speed
- 6mph
- Field efficiency
- 70%
20.4ac/h
Open with these valuesHow it's calculated
acres/hour = width (ft) × speed (mph) × FE% ÷ (8.25 × 100)
- StepEnter the width you actually cover in one pass, in feet.
- StepEnter your working speed in miles per hour.
- StepEnter field efficiency — the share of the hour spent covering new ground.
- ResultRead the rate; its inverse is the hours one acre takes.
What this number means
Acres per hour is a machine's field capacity: how much ground its working width sweeps at its working speed, minus the time it does not spend covering new ground. Iowa State University Extension writes the theoretical capacity as width in feet times speed in miles per hour divided by 8.25, then scales it by the field efficiency in percent. The 8.25 is not a fudge factor. It is 43,560 square feet per acre divided by 5,280 feet per mile, which turns foot-miles per hour into acres per hour, and it never changes. Field efficiency is where the honesty sits. It is the share of the hour actually spent covering new ground, and it absorbs overlapping passes, turning at the ends, refilling, unplugging, and stopping to check the machine. The publication's own table runs from 55 to 85 percent, with 80 percent a fair guess for open ground and less for a small yard full of beds and trees. The preset — a 5-foot deck at 5 mph and 80 percent — comes to 2.4 acres per hour, so one acre takes about 25 minutes. Doubling the width doubles the rate, and so does doubling the speed, until cut quality or safety stops you. What the formula cannot see is the ground itself: wet or tall grass, slopes, awkward headlands, and the walk back to the fuel can. Time a few real runs, solve backwards for efficiency, and use that figure instead of a table value.
Where 8.25 comes from
Iowa State University Extension derives it by dividing the 43,560 square feet in an acre by the 5,280 feet in a mile. Both numbers are definitions, so the factor never changes.
Efficiency is not a rounding allowance
It is the share of the hour spent covering new ground, and it swallows overlap, turns, refilling, and stops. Iowa State lists 55 to 85 percent for real implements.
Measure your speed with a stake and a watch
The publication gives a field method: mark 88 feet, time the drive, and speed in mph is 60 divided by the seconds you took. Twelve seconds means 5 mph.
One rate, three readings
Hours per acre is one divided by the rate. Square feet per hour is the rate times 43,560, and the time for a job is its acreage divided by the rate.
Commonly misread
My deck is 60 inches, so I enter 60.
The field is in feet: a 60-inch deck is 5 feet. Enter the width you really cover, which is less than the deck once you overlap passes.
Efficiency is 100% because I never stop.
Even a driver who never stops loses ground to overlap and to turning at the ends. Iowa State's table puts real implements between 55 and 85 percent.
Going twice as fast always doubles the acres per hour.
The arithmetic says yes, but the ground does not: past a point the cut degrades, the machine plugs, or efficiency drops. Speed only pays while the quality holds.
This only works for lawn mowers.
It is the standard field-capacity formula for any implement with a working width and a travel speed. The reference rows come from farm machines.
Reference table
| Machine and settings | Acres per hour |
|---|---|
| Fertilizer spreader 40 ft, 6 mph, 70 % | 20.4 |
| Grain drill 10 ft, 6 mph, 70 % | 5.1 |
| Field cultivator 24 ft, 7 mph, 85 % | 17.3 |
| Secondary disk 24 ft, 6 mph, 83 % | 14.5 |
| Rotary mower conditioner 14 ft, 7 mph, 80 % | 9.5 |
| Rake 20 ft, 7 mph, 80 % | 13.6 |
| Manure spreader 30 ft, 6 mph, 60 % | 13.1 |
Questions
How do you calculate acres per hour?
Multiply the working width in feet by the speed in miles per hour and by the field efficiency in percent, then divide by 825. A 5-foot deck at 5 mph and 80 percent gives 2.4 acres per hour.
Why divide by 8.25?
Because an acre is 43,560 square feet and a mile is 5,280 feet, and 43,560 divided by 5,280 is 8.25. It converts feet times miles per hour into acres per hour.
What field efficiency should I use?
Iowa State's table lists 55 to 85 percent for real implements. Use around 80 percent for open ground with long passes and less for small, irregular areas full of obstacles.
How long does one acre take?
One hour divided by the rate. At 2.4 acres per hour an acre takes about 25 minutes, and at 9.5 acres per hour about six minutes.
Does this work for tractors and implements, not just mowers?
Yes — it is the standard field-capacity formula for anything with a working width and a travel speed. The reference table is taken straight from a farm-machinery publication.
How do I measure my ground speed?
Mark off 88 feet, drive between the stakes, and count the seconds. Your speed in mph is 60 divided by that count, so twelve seconds is 5 mph.
Sources and last check
Information, not professional advice.