How many HP does a woodchipper need?
The rule of thumb is 3–4 HP per inch of branch diameter. Use our free calculator below for your exact setup, then scan the complete sizing chart.
HP requirements are one of the most-misunderstood parts of woodchipper sizing. Engine HP and PTO HP are different numbers. Wood species changes the working requirement. Feed type eats a few HP on top. The calculator below accounts for all three.
Woodchipper HP calculator
Tell us what you’ll chip. We’ll calculate the minimum and comfortable HP, then match woodchippers from our reviews that fit your spec.
Reading: A 6-inch hardwood chipper needs a minimum of 26 pto hp and runs comfortably at 35 pto hp or more. Tractor PTO HP is typically 10–15% lower than rated engine HP.
- 6″Check priceWoodland Mills · PTO-driven, 20–65 HP tractor · Self-feed · $2,999
- 6″Check priceWoodmaxx · PTO-driven, 25–65 HP tractor · Self-feed · $3,195
- 8″Check priceWoodmaxx · PTO-driven, 25–70 HP tractor · Self-feed · $3,995
Engine HP vs PTO HP — why the numbers differ
Tractors advertise engine HP (measured at the crankshaft). Chippers care about PTO HP (the HP that reaches the output shaft). Drivetrain losses reduce this by 10–15%.
A 35 HP engine tractor produces roughly 30 PTO HP. A 50 HP engine tractor produces ~43 PTO HP. Always size by PTO HP, not engine HP.
Hydraulic feed changes the math
Hydraulic-feed chippers draw 2–4 HP for the feed pump, so usable chipping HP is that much lower than rated PTO HP. This is why a 30 HP tractor on an 8-inch hydraulic chipper like the Woodmaxx WM-8H is at the absolute minimum — almost all available HP goes to chipping, not feeding.
Wood species effect on HP requirement
Dense seasoned hardwood (oak, hickory, maple) requires 25–40% more chipping HP than softwood (pine, spruce) or green hardwood. Most manufacturer specs are rated for seasoned hardwood — running below spec on softwood is usually fine. For a self-powered option that handles hardwood without borrowing tractor HP, see the MechMaxx DCH7 (22 HP Honda GX).
Complete PTO HP sizing chart (by branch diameter)
| Max branch | Softwood — min / comfortable pto hp | Mixed — min / comfortable pto hp | Hardwood — min / comfortable pto hp |
|---|---|---|---|
| 3″ | 8 / 11 HP | 11 / 14 HP | 13 / 18 HP |
| 4″ | 11 / 15 HP | 14 / 19 HP | 18 / 24 HP |
| 5″ | 14 / 18 HP | 18 / 24 HP | 22 / 30 HP |
| 6″ | 16 / 22 HP | 21 / 28 HP | 26 / 35 HP |
| 7″ | 19 / 26 HP | 25 / 33 HP | 31 / 41 HP |
| 8″ | 22 / 29 HP | 28 / 38 HP | 35 / 47 HP |
| 9″ | 25 / 33 HP | 32 / 43 HP | 39 / 53 HP |
Values are tractor PTO HP after drivetrain losses. Rated engine HP is typically 10–15% higher — a 35 HP engine tractor produces roughly 30 PTO HP.
Complete gas engine HP sizing chart (by branch diameter)
| Max branch | Softwood — min / comfortable engine hp | Mixed — min / comfortable engine hp | Hardwood — min / comfortable engine hp |
|---|---|---|---|
| 3″ | 7 / 9 HP | 8 / 11 HP | 10 / 14 HP |
| 4″ | 9 / 12 HP | 11 / 15 HP | 14 / 19 HP |
| 5″ | 11 / 15 HP | 14 / 19 HP | 18 / 24 HP |
| 6″ | 13 / 18 HP | 17 / 23 HP | 21 / 28 HP |
| 7″ | 15 / 21 HP | 20 / 26 HP | 24 / 33 HP |
| 8″ | 17 / 24 HP | 22 / 30 HP | 28 / 38 HP |
| 9″ | 20 / 27 HP | 25 / 34 HP | 32 / 43 HP |
Values are rated engine HP on the chipper itself. Honda GX commercial engines deliver closer to rated HP than generic engines under load.
Frequently asked questions
- What HP do I need to chip 6-inch branches?
- For PTO: 25 PTO HP minimum, 30–45 PTO HP comfortable. For gas engine chippers: 15 HP engine minimum (like the MechMaxx B150). These numbers assume seasoned hardwood — green softwood can run on 25–30% less.
- Is 30 HP enough for an 8-inch PTO chipper?
- At the absolute minimum, yes — the Woodmaxx WM-8H is rated down to 30 HP. You'll feel the limit on hardwood and the hydraulic-feed pump draw. For comfortable 8-inch chipping, 40 PTO HP is the right target.
- What's the HP difference between PTO and gas chippers?
- Gas chippers need less rated HP for the same capacity because their engines deliver HP directly to the flywheel without drivetrain losses. A 7-inch gas chipper runs on 22 HP (Honda GX); an equivalent 7-inch PTO chipper wants 28+ PTO HP (35+ engine HP).
- Does wood species actually affect HP requirements?
- Yes. Dense seasoned hardwood can require 25–40% more chipping HP than softwood or green wood. Our calculator applies a 1.25x multiplier for hardwood and 0.78x for softwood — matching manufacturer recommended-range guidance.
- Can I run a chipper at exactly the minimum HP?
- Yes, but feed rate will be slow on dense material and the flywheel will bog more easily on knots. For regular use, sizing 25–50% above the minimum is where tractors and engines feel comfortable.