TWA Calculator - QHSE Link

Time-Weighted Average (TWA) Calculator

Calculate a worker’s average contaminant exposure over a full shift and compare it with an Occupational Exposure Limit (OEL).

Formula: TWA = (C₁T₁ + C₂T₂ + … + CₙTₙ) ÷ Total shift duration

Total shift duration

min

Default: 480 minutes (8 hours).

Time unit Use the same unit for the shift and all periods.

Concentration unit This label does not change the calculation.

Occupational Exposure Limit (optional) Enter the applicable OSHA PEL, ACGIH TLV, or other OEL.

Exposure periods

Enter concentration and duration for each exposure period.

Period	Concentration (C)	Duration (T)	C × T

TWA assessment—

Enter the exposure data and select Calculate.

Important: Use the exposure limit and reference period required by the applicable regulation or professional standard. This calculator does not replace competent occupational hygiene assessment.