How many acres can a disc harrow cover per hour? A 14 foot disc harrow covers about 6.79 acres per hour at 5 miles per hour and 80 percent efficiency. An 8 foot disc harrow covers about 3.88 acres per hour at the same speed and efficiency, and a 20 foot disc harrow covers about 9.70 acres per hour.
A disc harrow is faster than a plow and a rotary tiller, because it works shallower and covers more width. It cuts and mixes the top layer of soil, and it leaves a seedbed ready for a cultivator pass or for planting. This guide works out the rate by width, by speed, and by efficiency.
Table of Contents
What a Disc Harrow Does
A disc harrow uses gangs of round discs to cut, lift, and mix soil. The discs cut residue, break clods, and level the surface in one pass. It is a secondary tillage tool in most plans, used after a plow or a chisel plow, and before a field cultivator or a planter.
A disc harrow is not a plow. A plow turns soil over in a deep pass, while a disc harrow works the top layer. For the wider tillage picture, see the tillage equipment productivity guide.
The Formula for a Disc Harrow
Acres per hour is width in feet times speed in miles per hour times efficiency, divided by 8.25. The constant 8.25 is 43560 divided by 5280. Efficiency is written as a decimal, so 80 percent is 0.80 and 70 percent is 0.70.
Take the 14 foot disc harrow from the verified table. Width times speed is 14 times 5, which equals 70. Multiply by efficiency as a decimal. 70 times 0.80 equals 56. Divide by 8.25. 56 divided by 8.25 equals 6.79 acres per hour after rounding. Divide acres by acres per hour to get time. The whole number is hours, and the decimal part times 60 is minutes. All times here are worked out from the unrounded rate, so checking them with the rounded rate in the text gives a slightly different result.
How Many Acres by Disc Harrow Width
Speed and efficiency stay fixed in the table below, so width is the only input that moves. Every row uses 5 miles per hour and 80 percent efficiency. A wider disc harrow covers more acres per hour, and minutes per acre fall as width rises.
| Disc harrow width | Acres per hour | Minutes per acre | Hours for 50 acres |
|---|---|---|---|
| 8 ft | 3.88 | 15.5 | 12.89 |
| 10 ft | 4.85 | 12.4 | 10.31 |
| 12 ft | 5.82 | 10.3 | 8.59 |
| 14 ft | 6.79 | 8.8 | 7.37 |
| 20 ft | 9.70 | 6.2 | 5.16 |
Read the table from your disc harrow width. An 8 foot disc harrow covers 3.88 acres per hour, and a 20 foot disc harrow covers 9.70. The step from 8 foot to 20 foot saves 7.73 hours on 50 acres. That saving holds only when the wider disc harrow can keep the same speed and efficiency on your soil. A disc harrow too wide for the tractor will slow down in heavy soil, and the rate falls with it.
How Speed Changes a Disc Harrow Rate
In the formula, speed carries the same weight as width, so a faster pass covers more acres per hour in direct proportion. The table below keeps a 14 foot disc harrow at 80 percent efficiency fixed and changes speed only.
| Speed in miles per hour | Acres per hour | Minutes per acre |
|---|---|---|
| 4 | 5.43 | 11.0 |
| 5 | 6.79 | 8.8 |
| 6 | 8.15 | 7.4 |
| 7 | 9.50 | 6.3 |
Moving from 4 to 7 miles per hour lifts the rate by 4.07 acres per hour. That gain holds only when the higher speed still cuts evenly across the full width. Too slow, and the discs drag without cutting cleanly. Too fast, and the discs can throw soil and leave ridges. Use the speed where the cut stays even, not the fastest speed the tractor can reach.
How Efficiency Changes a Disc Harrow Rate
Of the three inputs, efficiency is the one most people guess, and it is the one that most often explains a job that runs longer than the plan. The table below keeps a 14 foot disc harrow at 5 miles per hour fixed and changes efficiency only.
| Efficiency | Acres per hour | Minutes per acre |
|---|---|---|
| 70 percent | 5.94 | 10.1 |
| 80 percent | 6.79 | 8.8 |
| 90 percent | 7.64 | 7.9 |
The gap between 70 percent and 90 percent is 1.70 acres per hour. Use 80 percent as a planning start for a fairly open field. Go lower for a small or irregular field with many turns, and higher only for a large open rectangle. If you are not sure, use the lower efficiency. The guide on understanding field efficiency shows how turns and overlap make up the efficiency figure.
How Many Acres Can a Disc Harrow Cover Per Hour
Use the 14 foot rate of 6.79 acres per hour to plan common jobs. Twenty acres takes 2.95 hours, or about 2 hours and 57 minutes. Fifty acres takes 7.37 hours from the unrounded rate, or about 7 hours and 22 minutes. Fifty five acres takes 8.10 hours, or about 8 hours and 6 minutes. One hundred acres takes 14.73 hours.
That 55 acre time is the secondary question in this guide. A large disc harrow finishes 55 acres in one working day, while a small moldboard plow would need many days for the same acres.
Small Tractor and Large Tractor Rates, Kept Separate
Disc harrow rates for a small tractor and a large tractor are different, and they should not be mixed in one row. A small tractor setup in this guide is an 8 foot or 10 foot disc harrow at 5 miles per hour and 80 percent efficiency, giving 3.88 or 4.85 acres per hour. A large tractor setup is a 14 foot or 20 foot disc harrow at the same speed and efficiency, giving 6.79 or 9.70 acres per hour. Those small and large labels are this guide’s width bands only. The general tilling guide How Many Acres Can You Till Per Hour uses a different split: its small disc harrow is 5 feet wide at 3.5 miles per hour for 1.48 acres per hour, while its large 14 foot rate matches the 6.79 rate used here.
A very wide disc harrow needs a large tractor and a large field. A 25 foot disc harrow at 6 miles per hour and 80 percent efficiency would cover 14.55 acres per hour, because 25 times 6 times 0.80 equals 120, and 120 divided by 8.25 equals 14.55. Pick the row that matches your tractor and your disc harrow width, and do not use a large rate for a small setup.
Two More Disc Harrow Rates at Stated Inputs
Two more worked rates show why inputs matter, using only the formula in this guide. An 18 foot disc harrow at 5.5 miles per hour and 80 percent efficiency covers 9.60 acres per hour, because 18 times 5.5 times 0.80 equals 79.2, and 79.2 divided by 8.25 equals 9.60. At 5 miles per hour, the same 18 foot harrow at 80 percent efficiency covers 8.73 acres per hour. The half mile per hour of extra speed is worth about 0.87 acres per hour at that width.
A 10 foot disc harrow at 4 miles per hour and 75 percent efficiency covers 3.64 acres per hour, because 10 times 4 times 0.75 equals 30, and 30 divided by 8.25 equals 3.64. At 80 percent efficiency, the same width and speed give 3.88 acres per hour. Efficiency alone explains the difference between the two figures, not a different formula, so always read the efficiency beside a rate before you use it.
What Changes Your Disc Harrow Rate
Disc angle sets the cut on a disc harrow. A steep gang angle bites deeper and mixes more residue, but it pulls harder and holds the speed down. A flat gang angle runs faster yet may only scratch the surface, so the finish can look level while the soil below stays untouched. Wet ground makes the discs smear and carry soil, and dry ground can make them skip across the surface.
Field layout sets the efficiency next. Long straight runs keep the gangs working most of the hour, while short runs with many turns spend much of the hour turning. A gang wider than the tractor can drag will slow in heavy ground. A shallow cut that runs fast is no saving if it leaves residue unmixed and the ground needs another pass.
Common Mistakes and Limitations
The first error is to plan from width and speed with efficiency left at 100 percent. That figure is the fastest rate the harrow could ever reach, not the rate it will reach in a real field. The second error is to plan from the fastest speed the tractor can reach. Plan from the speed where the discs cut evenly, because a rushed pass throws soil into ridges. The third error is using a wide harrow rate for a narrow harrow. Match the rate to the harrow in front of you.
The fourth error is running too fast and leaving ridges, then treating the second pass as free. It doubles the time on that ground, so a steady pass at an even cut is usually the faster day. The fifth error is to forget travel, hitching and breaks, which are real hours outside acres per hour. Treat the result as a planning figure, then check it against a timed disc harrow job.
Frequently Asked Questions
Q: How many acres can a disc harrow cover per hour?
A: A 14 foot disc harrow covers about 6.79 acres per hour at 5 miles per hour and 80 percent efficiency. An 8 foot disc harrow covers about 3.88, and a 20 foot disc harrow covers about 9.70.
Q: How do I work out acres per hour for a disc harrow?
A: Multiply width in feet by speed in miles per hour and by efficiency as a decimal, then divide the result by 8.25. For a 14 foot disc harrow at 5 miles per hour and 80 percent efficiency, that is 14 times 5 times 0.80 divided by 8.25, which equals 6.79.
Q: How long does it take a disc harrow to cover 50 acres?
A: With a 14 foot disc harrow at 5 miles per hour and 80 percent efficiency, 50 acres takes 7.37 hours, or about 7 hours and 22 minutes. With a 20 foot disc harrow it takes about 5.16 hours.
Q: How long does it take a disc harrow to cover 55 acres?
A: At 6.79 acres per hour, 55 acres takes about 8.10 hours. That is about one working day for a large disc harrow on a fairly open field.
Q: Is a disc harrow faster than a rotary tiller?
A: Yes, in most cases. A 14 foot disc harrow covers 6.79 acres per hour, while a 6 foot rotary tiller covers 1.36 at its normal slow speed.
Q: Can I just go faster with a disc harrow?
A: No, not beyond the speed where the cut stays even. Too fast, and the discs can throw soil and leave ridges, which often needs a second pass.
Plan From Your Disc Harrow Width, Speed, and Efficiency
A disc harrow rate is not one fixed number. It is a result from harrow width, ground speed and efficiency for one setup in one field. Find your disc harrow width, hold a speed where the cut is even, and pick an efficiency that matches the field. Work out the time from the rate, then add travel, hitching and breaks. Run your own numbers through the Tilling Acres Per Hour Calculator before the next disc harrow job.
