Every tractor brochure leads with a horsepower number, and it is always the most flattering one available. Here is where that number comes from, how much of it survives the trip to the back of the tractor, and which number to compare instead. We ran the math on the hundreds of tractors in our database to find out.
One tractor, three horsepower numbers
When a brochure says "48 HP," that number was measured at one of three places, and the difference between them is not small:
Gross engine HP is the engine alone on a test stand: no cooling fan, no alternator, no hydraulic pump stealing power. It is the biggest legitimate number a manufacturer can print, which is why it is the one on the brochure cover.
PTO HP is what arrives at the shaft that spins your rotary cutter, tiller, or baler, after the engine has paid for its own cooling, charging, and hydraulics, and after the driveline has taken its cut. This is the number your implements live on.
Drawbar HP is pulling power at the hitch, measured under load. It matters for ground-engaging work like plowing, but for the loader-and-mower work most compact owners do, it barely enters the conversation. We cover why below.
One owner reviewing his TYM T474 after 250 hours put the gap in plain terms: the tractor is sold as 48.8 horsepower, but "the rear PTO is roughly 38 to 40 horsepower. There's people that put this on a dyno and have come out around 40." The gap is everywhere once you look for it: Kubota's LX3310 is rated 30.8 gross horsepower and 27 at the PTO, and that 12% loss counts as one of the tighter spreads in the industry. That is not a defect. That is how tractors work. The problem is that nobody tells you at the dealership.
We measured the gap across our whole database
We pulled the published engine and PTO ratings for every tractor in our database that lists both: hundreds of models across 12 brands. The result: about 19% of brochure horsepower never reaches the PTO shaft. Nearly a fifth, gone before it does any work. And the gap is not consistent:
| Brand | Models | Avg loss | Range |
|---|---|---|---|
| Mahindra | 31 | 23.0% | 13-31% |
| Rural King | 5 | 21.5% | 13-28% |
| John Deere | 28 | 21.3% | 11-30% |
| New Holland | 22 | 20.8% | 12-30% |
| Yanmar | 16 | 20.3% | 12-27% |
| Bobcat | 19 | 20.1% | 10-27% |
| Bad Boy | 8 | 19.6% | 8-28% |
| TYM | 37 | 18.6% | 8-30% |
| Kubota | 29 | 17.8% | 12-24% |
| Case IH | 19 | 17.4% | 13-30% |
| LS Tractor | 63 | 17.3% | 10-31% |
| Kioti | 55 | 17.2% | 8-27% |
Read this table carefully, because it does not say Mahindra builds inefficient tractors. It says the brochure number is not measured on a level field. Brands quote different rating standards, round differently, and some rate their PTO numbers conservatively on purpose. One owner four years into the same 48 horsepower machine noticed exactly that: his book claims 32 PTO horsepower, but as he put it, the manufacturer is "very conservative with that, they just say thirty-two across" the board. The lesson isn't which brand to avoid. The lesson is that "48 HP" from one brand and "48 HP" from another are different machines at the shaft, and only the PTO numbers are worth comparing. Notice where the big names land, too: Kubota runs one of the tightest average gaps in our data, while John Deere sits among the widest. The premium badge does not buy you a smaller loss; reading the PTO line does.
Why the brochure number is the big one
Horsepower ratings follow published standards, and the standards disagree on what to include. SAE J1995 and ISO 14396 measure gross power, the bare engine with no accessories. SAE J1349 and ISO 9249 measure net power, the engine as it sits in the tractor. Most compact tractor brochures quote a gross standard. That is a legal, accurate measurement of a configuration your tractor will never run in.
So when you compare a spec sheet quoting ISO 14396 gross against one quoting net power, you are comparing two different tests, not two different tractors. The PTO rating is the closest thing the industry has to a common yardstick, which is one more reason it is the number to trust.
There is one referee in this game: the Nebraska Tractor Test Lab, a public university lab that has been independently measuring tractor power since 1920. Their reports list measured PTO horsepower, drawbar pull, and fuel efficiency for the tractors they test, free to read. The catch for compact buyers: most tractors under 40 horsepower never go through the lab, so the class you are most likely shopping in is the one with the least independent data.
Why every subcompact is "24.9 horsepower"
Once you start looking, you will notice something odd: the market is wall-to-wall with tractors rated 24.5, 24.7, and 24.9 horsepower. That is not engineering coincidence. That is the EPA.
Federal Tier 4 emissions rules get significantly stricter for diesel engines above roughly 25 horsepower. Stay under the line and an engine meets the rules with simple hardware. Cross it and the tractor needs exhaust aftertreatment: a diesel particulate filter, regeneration cycles, more parts, more cost, more things to maintain. Manufacturers engineer to the line deliberately. A Kioti dealer walking a customer through the rules on camera lays it out: "Everything below 25 horsepower is not required to have any sort of emissions by the EPA," then comes simple emissions, then the full equipment. And a dealer showing off a 24.7 horsepower subcompact says the quiet part outright: the engine makes "24.7 horsepower intentionally to keep it under the EPA rating," with no regen system to babysit. Reviewers comparing models say the same thing from the buyer's side: the 25 horsepower class appeals precisely because those tractors are "more simplified without the emissions controls."
For you as a buyer, this cuts both ways. A 24.9 horsepower tractor is simpler and cheaper to own than a 26 horsepower tractor, and gives up almost nothing. But it also means the difference between a "25 HP" and a "35 HP" tractor is much bigger than 10 horsepower: it is a different regulatory class, a different engine strategy, and usually a different weight class too.
How much PTO horsepower do you need?
The rule of thumb for rotary cutters is about 5 PTO horsepower per foot of cut. A 5-foot cutter wants roughly 25 PTO horsepower; a 6-footer wants 30. Run that math against the table above and the classic mistake becomes obvious: a "35 horsepower" tractor delivers somewhere around 28 at the shaft, which handles a 5-foot cutter well and a 6-footer only in light grass. The 7-foot cutter that pins right onto the 3-point hitch will stall it in anything heavy. Buy the implement against the PTO number, never the brochure number.
Tillers, balers, and big flail mowers follow the same logic: check the implement's required PTO horsepower and leave margin. One owner running a 62-inch flail on a 25 horsepower tractor with the cab air conditioning on noted the AC itself was "putting an extra draw on the horsepower resources." He is right. Everything on the tractor eats from the same plate.
The 25 horsepower tractor with 19 horsepower
If you want to watch this trap catch someone in real time, there is a thread on a popular tractor forum titled, in full: "5' PTO Tiller for 25HP Tractor. 19HP to PTO." The title is the whole story. The owner has a 25 horsepower tractor. The shaft has 19. The 5-foot tiller he wants needs roughly 25 at the shaft. Six horsepower evaporated between the brochure and the dirt, and now the implement that "matches his tractor" does not match his tractor.
The replies are full of people who learned it the expensive way. One owner: "my previous tractor was underpowered for the mower. It sucked... Ok in lite stuff. It was 19hp, 16pto-hp with a 4' rotary." Another, after upgrading: his new machine is "40 hp (35 PTO) with a 6' mower. It is soooooo much nicer to have a little extra HP... than to be under powered." Nobody in these threads regrets the margin. Everybody regrets the gap.
When horsepower is the wrong question
Here is the part the brochures skip entirely: for loader work, none of the three horsepower numbers matter much. Lifting is hydraulic flow and pump pressure; stability is frame weight and ballast. One long-time owner shopping for exactly this said it best: "I don't care about having a ton of horsepower. I care about being able to lift heavy."
The manufacturers quietly agree. An owner who traded up to a 65 horsepower John Deere pointed out on camera that its loader "is the same body and loader that is used on their 45 horsepower" models. Deere does not size loaders by engine horsepower, and neither should you.
The same goes for traction work. Pulling is limited by weight and tires long before it is limited by power, which is why a heavier 40 horsepower tractor will out-pull a lighter 47 in the real world. If your week is loader chores, snow, and driveway grading, compare weight, lift capacity, and hydraulic flow between machines, and treat horsepower as a tiebreaker.
And if you are wondering whether skimping hurts later: a Kioti CK4010 owner's one-year review admitted the machine was "slightly underpowered for what I wanted to do." Regret runs in one direction. Nobody has ever complained about having five extra PTO horsepower.
The short version
- Ignore gross engine horsepower. It is a test-stand number.
- Compare tractors by PTO horsepower. It is the closest thing to a fair fight, and it is what your implements see. Expect it to run roughly 17-23% below the brochure number depending on brand.
- Size implements against PTO horsepower with margin: about 5 PTO HP per foot of rotary cutter.
- For loader-first tractors, compare weight, lift capacity, and hydraulic flow instead. Horsepower is the tiebreaker, not the headline.
- The 25 horsepower cluster is an EPA line, not a coincidence. Under it means simpler ownership; over it means emissions equipment. Decide which side of the line your work needs before you fall in love with a spec sheet.