A 15 foot bush hog acres per hour rate is 6.14 acres per hour at 4.5 miles per hour and 75 percent efficiency. At 5 miles per hour with the same efficiency it is 6.82 acres per hour, and at 3 miles per hour it is 4.09 acres per hour. See the table for other speeds.
Use the table to find your row, then use the examples to turn that rate into hours.
Table of Contents
How the 15 Foot Rate Is Worked Out
Acres per hour equals width in feet multiplied by speed in miles per hour multiplied by efficiency, divided by 8.25. Efficiency is a decimal here, so 75 percent becomes 0.75. The constant 8.25 comes from 43560 divided by 5280.
Check the formula against the homepage example. A 6 foot cutter at 4.5 miles per hour and 75 percent efficiency gives 2.45 acres per hour, which matches the Acres Per Hour Calculator with the same inputs. If your result differs, check efficiency first.
For a 15 foot cutter at the same speed and efficiency, 15 multiplied by 4.5 multiplied by 0.75, divided by 8.25, gives 6.14 acres per hour when rounded. The full result before rounding is 6.136 acres per hour.
In metric units, the same cutter at 4.5 miles per hour and 75 percent efficiency gives 2.48 hectares per hour.
Efficiency is the share of the working hour spent actually cutting, after time lost to turning, overlap, and stopping. At 75 percent, about one quarter of the hour is lost. At 85 percent, only about 15 percent is lost. At 65 percent, more than one third is lost.
15 Foot Bush Hog Acres Per Hour by Speed and Efficiency
Read across a row for your speed, then down a column for your efficiency.
| Speed in miles per hour | Rate at 65 percent efficiency | Rate at 75 percent efficiency | Rate at 85 percent efficiency |
|---|---|---|---|
| 3 | 3.55 acres per hour | 4.09 acres per hour | 4.64 acres per hour |
| 3.5 | 4.14 acres per hour | 4.77 acres per hour | 5.41 acres per hour |
| 4 | 4.73 acres per hour | 5.45 acres per hour | 6.18 acres per hour |
| 4.5 | 5.32 acres per hour | 6.14 acres per hour | 6.95 acres per hour |
| 5 | 5.91 acres per hour | 6.82 acres per hour | 7.73 acres per hour |
| 6 | 7.09 acres per hour | 8.18 acres per hour | 9.27 acres per hour |
Raising speed from 3 to 6 miles per hour at 75 percent efficiency doubles the rate, from 4.09 to 8.18 acres per hour. Raising efficiency from 65 to 85 percent at 5 miles per hour raises the rate from 5.91 to 7.73 acres per hour, a large gain but not a doubling. A fast run with low efficiency can match a slower run with high efficiency, since 6 miles per hour at 65 percent gives 7.09 acres per hour, while 5 miles per hour at 85 percent gives 7.73.
A single number from another site can mislead. One competitor gives bush hog rates of 2 to 3.5 acres per hour only, and another gives one row at 2.2 acres per hour. Those figures may fit a smaller cutter or a slower speed, but they do not describe a 15 foot cutter at a normal working speed. At 4 miles per hour and 65 percent efficiency, a 15 foot cutter already reaches 4.73 acres per hour.
How the 15 Foot Rate Compares With a 6 Foot Cutter
The homepage example gives a direct comparison at the same speed and efficiency. A 6 foot cutter at 4.5 miles per hour and 75 percent efficiency gives 2.45 acres per hour, while a 15 foot cutter gives 6.14 acres per hour. The 15 foot cutter is 2.5 times as wide, because 15 divided by 6 equals 2.5, and the rate is also 2.5 times as large.
| Cutter width | Speed in miles per hour | Efficiency | Acres per hour |
|---|---|---|---|
| 6 foot | 4.5 | 75 percent | 2.45 |
| 15 foot | 4.5 | 75 percent | 6.14 |
The time saving is clear. 20 acres at the 6 foot rate of 2.45 acres per hour takes 8.16 hours, so about 8.2 hours. The same field at the displayed 15 foot rate of 6.14 acres per hour takes 3.26 hours, a saving of about 4.9 hours. A wider cutter needs a tractor that can handle it and room to turn it, and on a small field it may lose efficiency to turning, so the saving will be smaller.
What Changes the Rate in a Real Field
The speed in the table is the working speed while cutting, not the road speed between fields. Thick growth, rough ground and wet soil all force a slower speed, which lowers the rate in direct proportion. Dropping from 5 to 4 miles per hour at 75 percent efficiency cuts the rate from 6.82 to 5.45 acres per hour. Record the speed you actually held, not the speed you hoped to hold.
Efficiency is often the larger source of error. Long straight passes keep it high, because little time goes to turning. Short passes lower it, because every turn is time with no new ground cut. Overlap lowers it too, because ground cut twice counts once in the finished area but twice in the time spent.
Ground, growth and field shape change both inputs at once. Tall growth can force a second pass, rough or wet ground forces slower speed, and a square field with long passes beats a field broken into small pieces. Count turns and moves when you plan, not only total acres.
Worked Examples You Can Check
First, the main rate. A 15 foot cutter at 4.5 miles per hour and 75 percent efficiency gives 6.14 acres per hour, using the displayed rate of 6.14. Ten acres takes 1.63 hours, 20 acres takes 3.26 hours, 50 acres takes 8.14 hours, and 100 acres takes 16.29 hours. Those are cutting times only, so add time for travel, fuel and breaks.
Second, a faster speed. A 15 foot cutter at 5 miles per hour and 75 percent efficiency gives 6.82 acres per hour. Twenty acres takes 2.93 hours, and 50 acres takes 7.33 hours, a gain of about 20 minutes on 20 acres over the first example, if you can hold 5 miles per hour while cutting cleanly.
Third, the slow end of the range. A 15 foot cutter at 3 miles per hour and 65 percent efficiency gives 3.55 acres per hour. Ten acres takes 2.82 hours, and 20 acres takes 5.63 hours, about 1.7 times the time of the first example for the same 20 acres. The difference comes entirely from speed and efficiency.
How to Use the Calculator for a 15 Foot Cutter
Use the homepage calculator on the homepage to check any rate. Enter 15 as the width in feet, enter your working speed in miles per hour, and enter efficiency as a percent. It uses the same formula as this guide, so it should match the table for the same inputs.
For a cutter specific check, use the Bush Hog Acres Per Hour Calculator as well. Run the same inputs through both tools and compare the results. They should agree, because they use the same formula.
For background, read the guide on what bush hogging is and the live post on bush hog rotary cutter productivity. This article does not repeat that definition or that general overview. When you have a rate, divide the field size by it to get cutting time, then add time for travel, fuel and breaks.
Common Mistakes and Limitations
The most common mistake is to use the theoretical rate as the field rate. The theoretical rate leaves out efficiency, so it assumes every minute is spent cutting. For a 15 foot cutter at 5 miles per hour, the theoretical rate is 9.09 acres per hour, while the field rate at 75 percent efficiency is 6.82 acres per hour. A second mistake is to copy a rate from another site without checking its width, speed and efficiency. A rate of 2.2 acres per hour may be correct for its own cutter, but it is not correct for a 15 foot cutter at 4.5 miles per hour and 75 percent efficiency.
A third mistake is to enter efficiency in the wrong form. The formula needs a decimal, so 75 percent must be entered as 0.75. Entering 75 instead makes the answer 100 times too large. A fourth mistake is to treat the rate as fixed for a whole job when the field changes part way through. Split the field into parts that match the ground and add the times together.
This guide has clear limits. The formula gives a rate for a stated width, speed and efficiency, and it does not know the state of your tractor or cutter, the moisture of the ground, or the thickness of the growth. It does not account for breakdowns. It does not set a safe speed for your ground, and it does not say which cutter size your tractor can handle.
Frequently Asked Questions
Q: How many acres per hour can a 15 foot bush hog cut?
A: At 4.5 miles per hour and 75 percent efficiency, a 15 foot bush hog acres per hour rate is 6.14 acres per hour. At 5 miles per hour it is 6.82 acres per hour, and at 3 miles per hour it is 4.09 acres per hour.
Q: How long does it take a 15 foot bush hog to cut 20 acres?
A: At 4.5 miles per hour and 75 percent efficiency, 20 acres takes 3.26 hours, or about 3 hours and 16 minutes. At 5 miles per hour it takes 2.93 hours, and at 3 miles per hour and 65 percent efficiency it takes 5.63 hours. Those are cutting times only.
Q: Is a 15 foot bush hog twice as fast as a 6 foot bush hog?
A: It is 2.5 times as fast when speed and efficiency stay the same, because 15 divided by 6 equals 2.5. At 4.5 miles per hour and 75 percent efficiency, the 6 foot cutter gives 2.45 acres per hour and the 15 foot cutter gives 6.14 acres per hour.
Q: What efficiency should I use for a 15 foot bush hog?
A: Use 75 percent as a starting point. Use 85 percent only for long straight passes on even ground with little stopping. Use 65 percent for short passes, rough ground, thick growth, or a field broken into small pieces.
Q: How do I work out bush hog acres per hour for a different speed?
A: Multiply width in feet by speed in miles per hour, multiply by efficiency as a decimal, and divide by 8.25. For a 15 foot cutter at 4 miles per hour and 75 percent efficiency, that gives 5.45 acres per hour. You can also use the Bush Hog Acres Per Hour Calculator linked in this guide.
Q: Why is my 15 foot bush hog slower than the table?
A: The most likely causes are a lower working speed, a lower efficiency, or both. Check the speed you actually held and the time lost to turns, overlap and stops. The fix may be fewer turns, less overlap, or a better route, rather than a higher speed.
Use 6.14 acres per hour at 4.5 miles per hour and 75 percent efficiency as your starting point, and work out the time for your field size before you start.
