Drive Shaft Sizingv1.0.0Method: Shaft Sizing

Drive Shaft Sizing Calculator

Calculate transmission shaft diameter under combined bending and torsion with the ASME shafting code allowable stress, keyway derating, and shock/fatigue factors.

Torsion & Bending Loads

Torque from

Transmitted Power (P)

Rotational Speed (N)

rpm

T = 98.8 N·m

Bending Moment (M)

N·m

Shaft Material

AISI 1045 Cold Drawn · Sy = 530 MPa, Sut = 630 MPa

Bending Shock Factor (Km)

Torsion Shock Factor (Kt)

Keyway at Section

Shaft Section

Shaft Section & Loads

ASME Transmission Shafting Code · combined bending and torsion

Results

Ready to calculate

Enter values and press Calculate to see results.

Reference Codes & Standards

ASME Shafting Code (1927)Governing Code

Code for Design of Transmission Shafting

Scope:Allowable shear stress min(0.30·Sy, 0.18·Sut), combined shock/fatigue factors Km and Kt, and 25 % keyway reduction. ASME B106.1M (1985) uses a different, fatigue-based method and is not what this calculator applies.

ANSI/AGMA 6001-E08Governing Code

Design and Selection of Components for Enclosed Gear Drives

Scope:Shaft and key stress calculations for mechanical power transmission.

Literature & Further Reading

[1]ASME Code for Design of Transmission Shafting (1927).
[2]Shigley's Mechanical Engineering Design — Shafts and Shaft Components.

Engineering Tips

Practical checks before using the result

Core Formulas

Shaft diameter

d³ = (16 / (π · τ_allow)) · √[(Km·M)² + (Kt·T)²]

ASME Code for Design of Transmission Shafting (1927); Km, Kt = combined shock and fatigue factors

Torsional deflection

θ = (584 · T · L) / (G · d⁴ · (1 − k⁴))

Twist angle in degrees for a solid (k = 0) or hollow (k = di/do) shaft

Strength sets the minimum diameter; stiffness (twist and deflection) often governs for long or gear-driving shafts.

Good practice

Check torsional stiffness: a common guideline for machinery shafts is ≤ 1° of twist over 20 diameters; long line shafting is often held to ≈ 0.26°/m (0.08°/ft).
Give shaft shoulders generous fillet radii (r/d ≥ 0.05–0.10) to keep stress concentration low.

Watch out

A keyway at the section reduces the allowable stress by 25 % (factor 0.75).
Check lateral critical (whirling) speed for long spans or high speeds (> 3000 rpm).

Not covered

Uses the classic Km/Kt allowable-stress method — not a full fatigue analysis with Marin factors and notch sensitivity (Shigley, ASME B106.1M).
Does not check bearing loads, lateral deflection, critical speed or key / spline stresses.