Work out time weighted average exposure instantly with clear inputs, formula shown and shareable results.
A time weighted average multiplies each measured concentration by the time it applied, sums the products, and divides by eight hours. Dividing by eight rather than by the sampled time is deliberate: unsampled parts of the shift are treated as zero exposure only if that is genuinely the case, otherwise the average over sampled time is the more honest figure.
Eight hour TWA
TWA = sum(Ci x Ti) / 8
Sampled average
Average = sum(Ci x Ti) / sum(Ti)
Preliminary estimate only. Exposure assessment must be performed by a qualified occupational hygienist to a recognised sampling standard.
TWA = sum(Ci x Ti) / 8. A time weighted average multiplies each measured concentration by the time it applied, sums the products, and divides by eight hours.
Divide by eight when the unsampled time is genuinely exposure free. If exposure continued unsampled, divide by sampled time and apply that concentration to the rest of the shift.
This calculator takes 4 inputs: Concentration in the first period, Duration of the first period, Concentration in the second period, Duration of the second period. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.