UV Dose For Disinfection Calculator

Work out uv dose for disinfection instantly with clear inputs, formula shown and shareable results.

About UV Dose For Disinfection Calculator

UV dose is intensity times exposure time, in millijoules per square centimetre. Water absorbs UV, so transmittance at 254 nm scales the delivered dose. Regulatory targets are typically 40 mJ/cm2 for 4-log virus inactivation in drinking water and 30 mJ/cm2 for wastewater reuse.

Formula

UV dose

Dose (mJ/cm2) = intensity (mW/cm2) x time (s) x UV transmittance

Worked example

With the default values below, UV Dose For Disinfection Calculator returns Delivered UV Dose of 42.240. Change any input above and every figure here is recalculated in your browser.

Inputs used

UV Intensityminimum 0 mW/cm2: 12 mW/cm2
Exposure Timeminimum 0 seconds: 4 seconds
UV Transmittance At 254 nmaccepts 0–100 %: 88 %
Target Doseminimum 0 mJ/cm2: 40 mJ/cm2

Results

Delivered UV Dose: 42.240
Nominal Dose Before Absorbance: 48.000
Time Needed For Target Dose: 3.7879
Compliance Status: Target dose achieved

Step by step

1Values used
2UV dose
3Delivered UV Dose= 42.240
4Nominal Dose Before Absorbance= 48.000
5Time Needed For Target Dose= 3.7879
6Compliance Status= Target dose achieved

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
UV disinfection systems used for potable water must be validated to a recognised protocol and monitored continuously for intensity, flow and transmittance.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

UV disinfection systems used for potable water must be validated to a recognised protocol and monitored continuously for intensity, flow and transmittance.

Frequently Asked Questions

Why does transmittance matter so much?

Dissolved organics, iron and colour absorb UV, reducing the dose reaching organisms in the far part of the reactor. A drop from 90% to 70% transmittance can halve the effective dose.

What about lamp fouling and ageing?

Quartz sleeve fouling and lamp output decline over life both reduce delivered dose. Validated reactors apply a lamp ageing and fouling factor, and intensity sensors monitor performance continuously.