Sizing tools
Implement to tractor, or tractor to implementWhat size tractor do I need?
Select an implement and working width to get the tractor horsepower it requires. In My tractor mode, enter engine horsepower to get the widest mower, tiller, disc, or plow the tractor can run.
Quick reference
Horsepower needed by implement and width
The table gives PTO and engine horsepower ranges for common implement sizes. It assumes medium soil, a front-wheel-assist tractor, typical field speeds, and an 85 percent working load.
| Implement | Width | PTO hp | Engine hp |
|---|---|---|---|
| Rotary cutter (brush hog) | 4 ft | 24 to 38 | 27 to 44 |
| Rotary cutter (brush hog) | 5 ft | 29 to 47 | 34 to 55 |
| Rotary cutter (brush hog) | 6 ft | 35 to 56 | 41 to 66 |
| Rotary cutter (brush hog) | 7 ft | 41 to 66 | 48 to 77 |
| Rotary cutter (brush hog) | 10 ft | 59 to 94 | 68 to 109 |
| Rotary cutter (brush hog) | 15 ft | 88 to 141 | 103 to 164 |
| Finish mower | 4 ft | 19 to 28 | 22 to 33 |
| Finish mower | 5 ft | 24 to 35 | 27 to 41 |
| Finish mower | 6 ft | 28 to 42 | 33 to 49 |
| Finish mower | 7 ft | 33 to 49 | 38 to 57 |
| Rotary tiller | 4 ft | 28 to 42 | 33 to 49 |
| Rotary tiller | 5 ft | 35 to 53 | 41 to 62 |
| Rotary tiller | 6 ft | 42 to 64 | 49 to 74 |
| Rotary tiller | 7 ft | 49 to 74 | 57 to 86 |
| Rotary tiller | 8 ft | 56 to 85 | 66 to 98 |
| Round baler (bale width) | 4 ft | 47 to 71 | 55 to 82 |
| Round baler (bale width) | 5 ft | 59 to 88 | 68 to 103 |
| Tandem disc harrow | 6 ft | 35 to 50 | 41 to 58 |
| Tandem disc harrow | 8 ft | 47 to 66 | 55 to 77 |
| Tandem disc harrow | 10 ft | 59 to 83 | 69 to 96 |
| Tandem disc harrow | 14 ft | 83 to 116 | 96 to 135 |
| Tandem disc harrow | 20 ft | 118 to 165 | 137 to 192 |
| Tandem disc harrow | 30 ft | 177 to 248 | 206 to 289 |
| Field cultivator | 10 ft | 39 to 64 | 45 to 75 |
| Field cultivator | 15 ft | 58 to 97 | 67 to 112 |
| Field cultivator | 20 ft | 77 to 129 | 90 to 150 |
| Field cultivator | 30 ft | 116 to 193 | 135 to 225 |
| Field cultivator | 40 ft | 155 to 258 | 180 to 300 |
| Chisel plow (12 in shank spacing) | 7 ft | 71 to 107 | 83 to 124 |
| Chisel plow (12 in shank spacing) | 9 ft | 92 to 138 | 107 to 160 |
| Chisel plow (12 in shank spacing) | 11 ft | 112 to 168 | 130 to 195 |
| Chisel plow (12 in shank spacing) | 15 ft | 153 to 229 | 178 to 266 |
| Chisel plow (12 in shank spacing) | 20 ft | 204 to 306 | 237 to 355 |
| Moldboard plow | 2.3 ft | 32 to 46 | 37 to 54 |
| Moldboard plow | 2.7 ft | 37 to 54 | 43 to 63 |
| Moldboard plow | 4 ft | 55 to 81 | 64 to 94 |
| Moldboard plow | 5.3 ft | 73 to 107 | 85 to 124 |
| Moldboard plow | 6.7 ft | 92 to 135 | 107 to 157 |
| Moldboard plow | 8 ft | 110 to 161 | 128 to 188 |
| Row-crop planter | 10 ft | 35 to 59 | 41 to 68 |
| Row-crop planter | 15 ft | 53 to 88 | 62 to 103 |
| Row-crop planter | 20 ft | 71 to 118 | 82 to 137 |
| Row-crop planter | 30 ft | 106 to 176 | 123 to 205 |
| Row-crop planter | 40 ft | 141 to 235 | 164 to 274 |
Method
How required horsepower is calculated
PTO-driven implements (mowers, tillers, balers) and planters: PTO hp = working width (ft) × hp per foot for the implement.
Pulled tillage tools: drawbar hp = draft (lb per ft) × soil factor × working width (ft) × speed (mph) ÷ 375. The soil factor is 0.75 for light soil, 1.0 for medium soil, and 1.3 for heavy soil. Drawbar hp is converted to PTO hp by dividing by the ASABE tractive ratio for the drive type on that surface (see the PTO horsepower calculator).
Required PTO hp = PTO hp ÷ 0.85, so the tractor runs the implement at about 85 percent of its available PTO power. Engine hp = required PTO hp ÷ 0.86 (PTO efficiency). In "My tractor" mode the same calculation runs in reverse to find the widest implement of each type.
Tractor listings by horsepower class:
FAQ
Frequently asked questions
What size tractor do I need for a 6 ft brush hog?
A 6 ft rotary cutter needs roughly 35 to 55 PTO horsepower, which is a tractor of about 40 to 65 engine hp. Grass and light weeds sit at the low end. Thick brush, saplings, and hilly ground need the high end.
Should I size a tractor to the implement exactly?
No. Plan to run an implement at about 85 percent of the tractor's available PTO power. That leaves headroom for hills, wet spots, and heavier crop, and keeps the engine out of constant full load. This calculator already includes that margin.
Why do pulled implements depend on soil and drive type?
Tillage tools are limited by draft, the pulling force they need. Heavy clay can need about 30 percent more draft than loam, and light sandy soil about 25 percent less. A 2WD tractor also loses more power to wheel slip than a front-wheel-assist or tracked machine, so it needs more engine power for the same pull.
How accurate are these horsepower numbers?
They are planning ranges from published rules of thumb and ASABE draft and tractive data, not guarantees. Depth, speed, residue, slope, and implement design all move the real number. Check the implement maker's minimum and maximum hp rating before buying, and never exceed the maximum on a PTO driveline.
Calculators
Other calculators
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Estimate PTO and drawbar horsepower from rated engine power for any drive type and surface.
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Calculate target weight per horsepower, ballast to add, and the front/rear axle split for a job.
Fuel Consumption & Cost Calculator
Estimate diesel use and cost per hour and per job from rated horsepower or a known burn rate.
HP to kW Converter
Convert between horsepower, kilowatts, and metric horsepower (PS) for tractor spec sheets.
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Estimate monthly payments, total interest, and total cost for fixed-rate equipment financing.
Rated horsepower, operating weight, and tire sizes for each model are listed in the tractor spec database. Models can also be browsed by manufacturer.