Power tools
Units: hp and kWPTO and drawbar horsepower calculator
This calculator estimates PTO horsepower and drawbar horsepower from a tractor's rated engine power. Drawbar horsepower is given for each drive type on concrete, firm, tilled, and soft ground.
Method
How PTO and drawbar horsepower are estimated
PTO hp = rated engine hp × 0.83 to 0.90. This range is the typical driveline efficiency for diesel farm tractors. The single estimate uses 0.86.
Drawbar hp = PTO hp × tractive ratio. The tractive ratio depends on drive type and surface. The ratios in the table are planning values from ASABE D497, which university extension guides also use to match tractors to implements.
| Surface | 2WD | MFWD (front-wheel assist) | Articulated 4WD | Tracks |
|---|---|---|---|---|
| Concrete | 87% | 87% | 88% | 88% |
| Firm untilled soil | 72% | 77% | 78% | 80% |
| Tilled soil | 67% | 73% | 75% | 78% |
| Soft or sandy soil | 55% | 65% | 70% | 75% |
Engine ratings vary by standard (gross, net, SAE, ISO, ECE), so the results are planning ranges. With PTO power known, implements can be sized with the tractor size calculator or set ballast with the ballast calculator.
Rated engine power is listed on most tractor spec pages. Browse by horsepower class:
FAQ
Frequently asked questions
How much PTO horsepower does a tractor have compared to engine horsepower?
Most diesel tractors deliver about 83 to 90 percent of rated engine power at the PTO shaft. The rest is lost in the transmission, hydraulic pump, and cooling fan. A 100 hp engine typically gives 83 to 90 PTO hp, with 86 hp a reasonable single estimate.
What is the difference between PTO horsepower and drawbar horsepower?
PTO horsepower is the power available at the rear shaft to drive mowers, balers, and tillers. Drawbar horsepower is the pulling power available at the hitch. It is always lower because tires slip and the tractor spends power moving itself. On tilled soil a 2WD tractor puts only about two thirds of its PTO power to the drawbar.
Why does drive type change drawbar horsepower?
Front-wheel assist, articulated four-wheel drive, and tracks spread the pull across more ground contact, so they slip less and convert more power into pull. The advantage grows on soft ground: on loose or sandy soil a tracked tractor can deliver about 75 percent of PTO power at the drawbar while a 2WD tractor manages about 55 percent.
Should I trust the PTO rating on a spec sheet or this estimate?
Use a measured rating when one is available. Nebraska Tractor Test reports and manufacturer PTO ratings are measured on a dynamometer and are more accurate than an estimate. This calculator is for tractors where only engine power is published, and for comparing machines on the same basis.
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Rated horsepower, operating weight, and tire sizes for each model are listed in the tractor spec database. Models can also be browsed by manufacturer.