UV Dose Calculator
UV dose is intensity times time. Enter your reactor’s average intensity and the water’s exposure time to get the delivered dose in mJ/cm² — then compare it with common targets below.
UV Dose
| Item | Value |
|---|
How the calculation works
Formula
UV dose (mJ/cm²) = average intensity (mW/cm²) × exposure time (s)
because 1 mW · s / cm² = 1 mJ/cm². This is the calculated (not validated) dose.
UV dose (mJ/cm²) = average intensity (mW/cm²) × exposure time (s)
because 1 mW · s / cm² = 1 mJ/cm². This is the calculated (not validated) dose.
| Benchmark | UV dose (mJ/cm²) |
|---|---|
| NSF/ANSI 55 Class A (point-of-use/entry) | 40 |
| NSF/ANSI 55 Class B (supplemental) | 16 |
| UVDGM / 40 CFR 141.720 — virus 4-log | 186 |
| UVDGM / 40 CFR 141.720 — Cryptosporidium 3-log | 12 |
| UVDGM / 40 CFR 141.720 — Giardia 3-log | 11 |
| DVGW — 4-log bacteria and virus | 40 |
Notes & limitations
UV dose targets from the EPA UV Disinfection Guidance Manual (UVDGM, 2006) Table 1.4 as codified at 40 CFR 141.720(d)(1), and NSF/ANSI 55. A calculated dose is not a validated dose — confirm the required dose with your state primacy agency.
- For LT2ESWTR disinfection credit, 40 CFR 141.720(d)(2) requires reactors to undergo validation testing — calculated intensity-times-time alone does not earn credit.
- UV transmittance, lamp fouling and aging, and hydraulics all reduce the delivered dose below the nameplate calculation; monitor per the manufacturer and state requirements.
- The 186 mJ/cm² virus 4-log value is driven by adenovirus, the most UV-resistant regulated virus — it is not a typo.
- This tool does not replace reactor validation or state approval for drinking-water disinfection credit.
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