NIH Guide Table 3.2 — Mouse Floor Area Minimums
The Guide for the Care and Use of Laboratory Animals (8th edition, 2011) Table 3.2 sets the minimum floor area per mouse for grouped housing:
- Mice under 10 g: 6 in2 per animal
- Mice 10–15 g: 8 in2 per animal
- Mice 15–25 g: 12 in2 per animal
- Mice over 25 g: 15 in2 per animal
- Breeding female with litter: 51 in2 minimum
Standard mouse cages used in most North American vivariums (Allentown NextGen 500, Tecniplast GR900) provide 75–140 in2 of usable floor space, which sets the practical animals-per-cage ceiling. The calculator divides cage area by per-animal area, taking the floor as the maximum.
Why Cage Density Matters
Crowded cages distort more than welfare metrics — they confound experiments. Specific failure modes include:
- Hierarchy stress: ranked-mouse studies show elevated corticosterone above 80% density
- Bedding contamination: ammonia accumulation accelerates with animal load
- Heat retention: brown-fat thermogenesis is suppressed in high-density cages, biasing metabolic studies
- IACUC violations: housing density audits are the most common AAALAC citation in academic vivariums
A planner that enforces NIH Guide minimums up front is the cheapest fix — moving animals after a citation costs days of vivarium staff time and risks losing study power.
