Woodchipper HP calculator
Enter your branch diameter, wood type, and power source. The calculator returns the minimum and comfortable HP, then matches chippers from our reviews that fit your spec.
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
The math behind the calculator
The base formula: PTO HP ≈ 3.5 × branch diameter (in) × wood multiplier. Gas engine chippers use 2.8 HP/inch because direct drive avoids drivetrain losses. Wood multipliers: softwood 0.78×, mixed 1.0×, hardwood 1.25×.
The “comfortable” HP is the minimum × 1.35 — the working range where feed rate stays consistent and the flywheel doesn’t bog on knots or hardwood. This matches manufacturer-recommended HP ranges within a few percent for all the chippers in our database.
Matched product recommendations filter our 19 reviewed models by: (1) correct power type, (2) maxBranchIn ≥ your requested size, (3) HP min ≤ comfortable HP + 5. Results are sorted by closest capacity match, then price.
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
- Is this HP calculator accurate?
- The formula matches manufacturer recommended-range tables within ±2 HP across 4–9 inch chipper sizes. It's most accurate for seasoned hardwood at full capacity (the default assumption). Green wood and softwood need 20–30% less HP — the calculator's softwood multiplier accounts for this.
- Engine HP vs PTO HP — which number should I enter?
- Select 'PTO tractor' if you're running a tractor chipper, and we'll size to PTO HP. Tractors lose 10–15% between engine and PTO, so a 35 HP engine tractor produces ~30 PTO HP. The calculator handles this distinction automatically.
- Does the calculator account for hydraulic feed draw?
- Partially — the comfortable-HP padding (35% above minimum) covers typical hydraulic pump draw of 2–4 HP. For commercial-grade hydraulic-feed chippers pushing hardwood, size up one tier above the comfortable number.
- Can I use this for commercial chippers (12+ inch)?
- The calculator covers 3–9 inch chippers, which is where homeowner and small-commercial buyers live. For 12+ inch commercial tow-behind chippers (Bandit, Vermeer, Morbark), work with your dealer — those machines often run on optimized engine-clutch-flywheel combinations that don't fit a generic formula.
- What chippers does the calculator match against?
- Our full review database: 7 Woodmaxx PTO chippers (MX-8500G+ through MX-9900), 3 Woodland Mills PTO chippers (WC46/WC68/WC88), 6 MechMaxx gas chippers (GS650 through CROBA TX1000), and 1 MechMaxx PTO unit (BX42S). Results link to full reviews with specs and affiliate price checks.