Estimate prop shaft diameters using torsion formulas and factors. Compare solid and hollow options confidently. Export results, inspect charts, and validate sizing decisions quickly.
The calculator first finds transmitted torque. When power and speed are entered, torque becomes T = 9550 × P / n, where power is in kW and speed is in rpm. If direct torque is entered, that value becomes the base torque.
Design torque then becomes Td = T × service factor × safety factor. This raises nominal torque to a more realistic design value for driveline shocks, start-up loads, and uncertainty.
For a solid circular shaft, the torsion relation used is τ = 16Td / (πd³). Rearranging gives the minimum diameter d = (16Td / (πτ))^(1/3).
For a hollow circular shaft with ratio k = di / do, the relation becomes τ = 16Td / (πdo³(1 - k⁴)). The calculator solves this for outer diameter and then multiplies by the ratio to get inner diameter.
It also estimates angle of twist from θ = TL / (JG). This helps compare stiffness, not only strength. Final engineering design should still verify fatigue, critical speed, balancing, splines, welds, keyways, and bearing spacing.
| Power (kW) | Speed (rpm) | Allowable Shear (MPa) | Design Torque (N·m) | Solid Diameter (mm) | Hollow Outer Diameter (mm) |
|---|---|---|---|---|---|
| 18 | 1500 | 60 | 208.57 | 26.06 | 27.30 |
| 45 | 1200 | 70 | 752.06 | 37.96 | 39.76 |
| 90 | 1000 | 80 | 2,062.80 | 50.83 | 53.24 |
| 140 | 850 | 90 | 4,530.07 | 63.52 | 66.53 |
Prop shaft sizing is a torsion problem, but real driveline behavior is broader. A shaft can pass a simple shear check and still fail because of fatigue, weld quality, imbalance, or excessive wind-up. This calculator helps with preliminary sizing by combining power, speed, allowable shear stress, service factor, safety factor, and geometric options in one place.
In many machines, power and rotational speed are known before torque is measured directly. The calculator handles that common workflow by converting power and rpm into transmitted torque. It then inflates that torque using service and safety factors. This is useful when machinery sees uneven loading, quick starts, reversing duty, shock, or uncertain operating conditions.
Solid shafts are simple, strong, and easy to manufacture. Hollow shafts often reduce mass while maintaining useful torsional capacity, but they need a larger outside diameter for the same allowable stress. That tradeoff is important in rotating systems where inertia, balancing, and packaging matter.
The twist estimate included here adds another engineering check. A shaft that is strong enough can still twist too much and create alignment, response, or vibration issues. Lower twist usually improves driveline feel and helps keep connected components working more predictably.
Treat the output as a design starting point. For production work, also review stress concentrations at shoulders, spline geometry, keyways, corrosion allowance, dynamic loading, bearing support spacing, and critical speed limits. Those checks turn a quick sizing study into a safer engineering decision.
It estimates minimum prop shaft diameter for torsional loading. It compares solid and hollow shafts, applies service and safety factors, and reports twist over the selected span.
Use direct torque when measured or given by design data. Otherwise enter power and speed, and the calculator converts them into transmitted torque automatically.
Real drivelines see shocks, clutch engagement, misalignment, and varying loads. The service factor raises nominal torque to a more realistic design level.
It adds margin for uncertainty, manufacturing variation, wear, and future operating changes. Severe or reversing duty usually needs a higher value.
It is inner diameter divided by outer diameter. Larger ratios reduce weight, but they require a bigger outside diameter for the same allowable stress.
No. Final design should also check fatigue, critical speed, buckling, splines, keyways, weld details, balancing, and bearing spacing.
It shows how much the shaft winds up over its length under torque. Excessive twist can hurt response, alignment, and durability.
Yes. You can enter horsepower, pound-feet, and psi. The calculator converts them internally and reports comparable sizing results.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.