How to estimate bush hog time for an overgrown field starts with a rate, not a guess. A 6 foot cutter at 4 miles per hour and 75 percent efficiency covers 2.18 acres per hour, so a 20 acre field takes about 9.2 hours of cutting time. Overgrown ground usually needs a lower rate.
Step 1 Measure the Field
Start with the area in acres. Measure the field, or use a known area from a map, a deed, or a previous cut. Do not guess the area from a drive past the field. A field that looks like 10 acres can be 8 acres or 12 acres, and that error alone can move the time by hours.
Check the access at the same time. Note the gate width, the route into the field, and the room to turn at the ends of the passes. A field that is hard to enter will lose time before cutting starts, and a field with no room to turn will lose efficiency on every pass. Those losses sit outside the formula, so note them now and add time for them later in the plan.
Step 2 Walk the Field First
Walk the field before you plan the rate. Tall growth hides rocks, stumps, holes, and wire, and those hazards force detours and lower efficiency. The task brief is clear on this point. Walk the field first, mark the hazards, and plan the route around them.
Step 3 Split the Field Into Zones
Split the field into zones that match the growth and the ground. A zone is a part of the field where speed and efficiency are about the same. Do not make zones too small, because a plan with twenty zones is hard to follow. Two or three zones are enough for most overgrown fields.
If a zone is very small, fold it into the zone beside it and use the slower rate for the combined area. It is better to plan a small rough patch at the rough rate than to plan it at the light rate and find it takes longer on the day. The split is a planning tool, not a survey. It only needs to be good enough to pick a honest rate for each part of the field.
Step 4 Pick Width, Speed, and Efficiency for Each Zone
Pick the cutter width first. Width is the working width, which is the actual cut swath minus overlap, not the machine width. On rough ground, overlap often rises, so working width falls. Measure the swath you actually cover and use that figure in the formula.
The Formula and the Verified Rates
Acres per hour equals width in feet times speed in miles per hour times efficiency, divided by 8.25. Efficiency is written as a decimal, so 75 percent is 0.75 and 65 percent is 0.65. The constant 8.25 comes from 43560 divided by 5280. To get time from a rate, divide acres by acres per hour. That gives hours, and the part after the decimal point times 60 gives minutes. Times in this guide use the unrounded rate, and only the final value is rounded.
| Cutter width | Rate at 75 percent efficiency | Rate at 65 percent efficiency |
|---|---|---|
| 6 foot | 2.18 acres per hour | 1.89 acres per hour |
Step 5 Work Out the Time Zone by Zone
Work out the time for each zone by dividing its acres by its rate, then add the times together. Do not average the rates first. Averaging rates gives the wrong total when the zones are different sizes, because a large slow zone matters more than a small fast zone.
Now change the rough zone to a slower speed. If the 8 rough acres need 3 miles per hour at 65 percent efficiency, the rate is 6 times 3 times 0.65, divided by 8.25, which equals 1.42 acres per hour. The light zone is 12 acres at 2.18 acres per hour, so its time is 12 divided by 2.18, which equals 5.50 hours. The time for those 8 acres is 8 divided by 1.42, which equals 5.64 hours. Add the light zone time of 5.50 hours, and the total becomes 11.14 hours, so about 11.1 hours. That is the value of the zone method. It shows where the time goes, and which zone is worth attention.
How to Estimate Bush Hog Time for an Overgrown Field: Worked Times
The table below uses a 6 foot cutter at 4 miles per hour, with light grass at 75 percent efficiency and rough pasture at 65 percent efficiency. Times are cutting time only. They do not include travel, fuel stops, or time spent clearing debris.
| Field size | Light grass time | Rough pasture time |
|---|---|---|
| 5 acres | 2.29 hours | 2.64 hours |
| 10 acres | 4.58 hours | 5.29 hours |
| 20 acres | 9.17 hours | 10.58 hours |
| 50 acres | 22.92 hours | 26.44 hours |
Step 6 Add Time Outside Cutting
The formula gives cutting time only. A complete estimate adds the time around cutting. Travel to the field, unloading, fuel stops, and time spent clearing debris all sit outside the cutting time. So do breaks, and so does time spent walking the field or marking hazards before the tractor starts.
Also allow time for a second pass in the thickest patches. Overgrown ground often leaves uncut stems on the first pass, and a second pass over part of the field is a normal part of the job, not a failure. If you plan a second pass over the rough zone only, work out that time as a separate zone and add it to the total. That keeps the plan honest and keeps the day from running over.
Step 7 Check the Estimate Before You Start
Check the estimate in three ways before you start. First, check the arithmetic. Divide acres by rate for each zone, add the zone times, and check that the zone areas add up to the total field area. A small addition error can move the total by hours on a large field.
Second, check the rates. Read each zone rate against its growth and ground, and check that a rough zone never uses the light grass rate. A rough zone planned at the light rate will understate the time, and the error grows with the size of the zone.
Third, check the estimate against a known job. If you cut a similar field last year, compare the planned rate with the rate you actually achieved. If the plan is much faster than the last real job, the plan is probably optimistic. Use the real rate, or use the lower efficiency, and rework the total. A plan based on a real rate from your own machine and your own ground is far more useful than a plan based on a general rate.
Common Mistakes in Overgrown Field Estimates
First, planning the whole field at the light grass rate. An overgrown field is rough by definition, so the light rate will understate the time. Use the rough rate for the rough parts, and use a slower speed where the growth is thick and woody.
Other mistakes are forgetting the walk through and counting only cutting time. Tall growth hides hazards, and hazards force detours. Walk the field first, mark stumps, rocks, holes, and wire, and plan the route around them. Travel, fuel, breaks, and a possible second pass all add time. List them, give each a time from your last job, and add them to the cutting total.
Frequently Asked Questions
Q: How to estimate bush hog time for an overgrown field?
A: Measure the field, walk it first, split it into zones by growth and ground, pick width, speed, and efficiency for each zone, divide each zone area by its rate, and add the zone times together. Then add travel, fuel, breaks, and any second pass time. A 6 foot cutter at 4 miles per hour and 75 percent efficiency covers 2.18 acres per hour, so 20 acres takes about 9.2 hours of cutting time on light grass.
Q: What rate should I use for an overgrown field?
A: Use 65 percent efficiency as a starting point for rough pasture at 4 miles per hour, which gives 1.89 acres per hour with a 6 foot cutter. Use a slower speed, for example 3 miles per hour, if the growth is thick, tall, and woody. At 3 miles per hour and 65 percent efficiency, the same cutter covers 1.42 acres per hour.
Q: How long does it take to bush hog 10 acres of overgrown ground?
A: With a 6 foot cutter at 4 miles per hour and 65 percent efficiency, 10 acres takes 5.29 hours of cutting time, because 10 divided by 1.89 equals 5.29. At 3 miles per hour and 65 percent efficiency, it takes 7.05 hours. Those times do not include travel, fuel, breaks, or a second pass.
Q: Should I split an overgrown field into zones?
A: Yes. Split it into parts where speed and efficiency are about the same, work out the time for each part, and add the times together. For example, 12 acres of light grass at 2.18 acres per hour takes 5.50 hours, and 8 acres of rough pasture at 1.89 acres per hour takes 4.23 hours, so the total is about 9.7 hours of cutting time.
Q: What efficiency band fits an overgrown field?
A: A small or irregular overgrown field fits the 55 to 65 percent band. An average field fits the 70 to 75 percent band. A large rectangular field fits the 80 to 85 percent band. The ideal band is 85 to 90 percent, and it is for ideal fields with GPS guidance, not for overgrown ground.
Q: Why is my overgrown field taking longer than the estimate?
A: The most likely causes are a lower working speed, a lower efficiency, or both. Check the speed you actually held, the time lost to turns, overlap, and stops, and whether a second pass was needed in thick patches. Record the real rate and use it for the next estimate on the same field.
Estimate Part by Part, Then Add the Day Around It
How to estimate bush hog time for an overgrown field is a sum, not a single rate. Measure the field, walk it, split it by growth and ground, pick a rate for each zone, and add the zone times together. Use 2.18 acres per hour for light grass and 1.89 acres per hour for rough pasture with a 6 foot cutter at 4 miles per hour, and use a slower speed when the growth demands it. Add travel, fuel, breaks, and any second pass, and check the result with the Acres Per Hour Calculator before you start. Check the rate with the Bush Hog Acres Per Hour Calculator and read the guide on how to calculate acres per hour and the guide on understanding field efficiency for the full method. For cost planning, use the live bush hogging cost calculator.
