Rodent Infestation Severity Calculator
Estimate the severity of a rodent infestation using observable signs, affected area, and environmental risk factors. The result guides appropriate response actions.
Formula
Infestation Severity Score (ISS) is a weighted composite of four sub-scores, each normalised to 0–100:
- Sign Score (SS, 30%):
SS_raw = (droppings × 0.40) + (gnaw × 0.25) + (tracks × 0.15) + (nests × 0.20)
SS_norm = min(SS_raw / 55 × 100, 100)
Reference maxima: 100 droppings/day, 40 gnaw marks, 20 tracks, 10 nests - Population Pressure Score (PPS, 25%):
PPS = min((sightings / 10) × 100, 100)
10 sightings/week represents maximum pressure - Density Score (DS, 20%):
density = sightings / area (rodents per sq ft per week)
DS = min((density / 0.05) × 100, 100)
0.05 rodents/sq ft/week is the severe threshold - Risk Factor Score (RFS, 25%):
RFS = min((food_access × 25) + (min(entry_points, 5) × 5) + min(duration_weeks × 2, 30), 100) - ISS = (SS × 0.30) + (PPS × 0.25) + (DS × 0.20) + (RFS × 0.25)
Severity Bands: 0–20 Minimal | 21–40 Low | 41–60 Moderate | 61–80 High | 81–100 Severe
Estimated Population: Derived from droppings (÷35–50 per rodent/day), nests (4–8 per nest), and sightings (×0.5–1.5 factor).
Assumptions & References
- A single mouse produces approximately 40–100 droppings per day; a rat produces 25–75 (Corrigan, R.M., Rodent Control, PCT Media, 2001).
- The 0.05 rodents/sq ft/week density threshold is adapted from commercial pest management severity indices used by the National Pest Management Association (NPMA).
- Food accessibility and entry points are primary drivers of infestation growth per CDC rodent control guidelines (CDC, 2023).
- Duration weighting reflects exponential population growth potential: a pair of mice can produce 200+ offspring in 4 months under ideal conditions (Timm, R.M., UC IPM, 2020).
- Population estimates are heuristic approximations; actual counts require professional trapping surveys.
- This calculator is for informational purposes only and does not replace a professional pest inspection.
- Weights and thresholds are based on integrated pest management (IPM) literature and may vary by rodent species (Mus musculus, Rattus norvegicus, Rattus rattus).