Power, Torque & Speed

Parallel Key Stress Calculator

Check nominal average stresses for one parallel key from actual torque and engagement. Supply your own allowable-stress basis; full shaft, hub, fatigue and fit requirements remain separate.

Default geometry is an editable illustration. Allowables are blank; no material recommendation or assembly approval.

CALCULATION SETUP

Inputs

Preset

Torque magnitude

Shaft diameter

Key width

Need an input value?

Key & Keyway Size Chart ↗Transfer width/height explicitly; enter actual contact and effective length separately.

Key height

Need an input value?

Key & Keyway Size Chart ↗Transfer width/height explicitly; enter actual contact and effective length separately.

Flank engagement basis

A cross-section lookup does not supply machining depth or actual flank contact.

Actual load-bearing flank height

Required with the actual-contact basis. Do not infer it from the key size chart.

Effective engaged length

Required for stress/capacity. Rounded ends and unengaged material are not effective contact; minimum-length mode can omit it.

User-supplied allowable shear stress

No default material allowables. One criterion produces only its individual result.

User-supplied allowable bearing stress

Both stresses are needed for the combined length/capacity criterion.

Available hub engagement length (optional)

Calculated locally in your browser. No sign-up or input upload.

CALCULATED VALUE

Results

Nominal average shear stress

13.227513 MPa1,918.488594 psi

Tangential force

10,000 N2,248.089431 lbf

Nominal average bearing stress

39.68254 MPa5,755.465783 psi

Effective shear area

756 mm²1.171802 in²

Effective flank contact area

252 mm²0.390601 in²

Actual b = 12 mm, h = 8 mm, e = 4 mm, effective L = 63 mm. Schematic only; no machining depth, fits, fatigue or full assembly approval is implied.

Calculation breakdown

Flank engagement basis: Actual flank engagement is user entered; never inferred from the cross-section chart.
Combined criterion: Unavailable: both user-supplied allowable shear and bearing stresses are required. No default material allowables.

Only the result summary and canonical link are shared. Inputs and free-form names are excluded.

Assumptions & checks

Nominal static single-key average-stress model only. Fatigue, stress concentrations, dynamic overload, shaft weakening, hub failure, unequal multiple-key sharing, fits and machining tolerances are excluded.

A calculated minimum or entered allowable criterion is not complete assembly safety/approval. No material allowable, purchased length or full keyway depth is inferred.

Combined length/capacity criterion is unavailable. Only individually supplied criteria are calculated.

Verify inputs & continue

Existing key cross-section lookup supplies width/height only. User enters actual contact, effective length and stress allowables; no invented machining geometry or material criteria.

Key & Keyway Size Chart

Use data for the actual component and operating conditions. Continue with the related calculations below after reviewing the selected result.

Formula

Static torque equilibrium and nominal average shear/contact stress for one key

F = 2T/D; τ = F/(bL); σ = F/(eL). With user-supplied criteria: Lshear = F/(bτallow), Lbearing = F/(eσallow); Lreq = max(Lshear,Lbearing) only when both are supplied. Tcapacity = min(τallow bLD/2, σallow eLD/2) only with both. e=h/2 is an explicit optional assumption, not a machining-depth fact.

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Torque magnitude: 200 N·m
Shaft diameter: 40 mm
Key width: 12 mm
Key height: 8 mm
Flank engagement basis: Actual user-entered contact height
Actual load-bearing flank height: 4 mm
Effective engaged length: 63 mm
User-supplied allowable shear stress: MPa
User-supplied allowable bearing stress: MPa
Available hub engagement length (optional): mm

Result

Nominal average shear stress: 13.227513 MPa
Tangential force: 10,000 N
Nominal average bearing stress: 39.68254 MPa
Effective shear area: 756 mm²
Effective flank contact area: 252 mm²

REAL INPUTS · CLEAR METHOD

Practical worked examples

Illustrative scenarios using this page’s calculation or verified reference model. Change the assumptions for your own job.

150 N·m, 30 mm shaft, 8 mm key

Given

Torque magnitude: 150 N·m
Shaft diameter: 30 mm
Key width: 8 mm
Key height: 7 mm
Flank engagement basis: Actual user-entered contact height
Actual load-bearing flank height: 3 mm
Effective engaged length: 45 mm
User-supplied allowable shear stress: 60 MPa
User-supplied allowable bearing stress: 120 MPa
Available hub engagement length (optional): mm

Calculation / lookup method

Result

Nominal average shear stress: 27.777778 MPa
Tangential force: 10,000 N
Nominal average bearing stress: 74.074074 MPa
Effective shear area: 360 mm²
Effective flank contact area: 135 mm²
Minimum length — supplied shear criterion: 20.833333 mm

Force is 10000 N; average shear is 27.777778 MPa and bearing 74.074074 MPa. These educational, user-supplied criteria give a governing length 27.777778 mm and nominal torque capacity 243 N·m. They are not material recommendations.

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Technical references for this calculation

Reference lookupKey & Keyway Size Chart

Frequently asked questions

Is effective length the nominal key length?

Not necessarily. Only the engaged torque-bearing length is used; rounded ends and unengaged portions require actual geometry review.

Is flank engagement always half the key height?

No. The half-height option is an explicit approximation. Actual load-bearing contact must come from the applicable assembly/machining geometry.

Why are allowable stresses blank?

Material, design basis, service and safety factors are application-specific. The tool does not invent universal allowable stresses or select a material.

What happens with only one allowable?

Its individual minimum length/capacity is shown. The combined criterion remains unavailable until both shear and bearing allowables are supplied.

Does meeting these stresses approve the assembly?

No. Average static key stresses exclude fatigue, stress concentrations, shaft/hub failure, fits, dynamic overload and unequal load sharing.

Reference data & method sources

ValiCalc key cross-section reference
Existing sourced width/height subset only. Explicit transfer clears actual contact and effective length for your review; no new proprietary table.