Question 1

What floor area does the NIH Guide require for rats?

Accepted Answer

The NIH Guide for the Care and Use of Laboratory Animals (8th ed., Table 3.3) sets minimum floor area per rat by weight class: <100 g requires 17 $	ext{in}^{2}$, 100–200 g requires 23 $	ext{in}^{2}$, 200–300 g requires 29 $	ext{in}^{2}$, 300–400 g requires 40 $	ext{in}^{2}$, 400–500 g requires 60 $	ext{in}^{2}$, and over 500 g requires 70 $	ext{in}^{2}$. These are floor area minimums for group-housed rats; nursing dam-with-litter combinations have separate (larger) requirements.

Question 2

Why do rats need so much more space than mice?

Accepted Answer

Adult laboratory rats are roughly 10× the body mass of adult mice and have very different motor patterns — they rear, climb, and dig much more than mice do. The NIH Guide reflects this by requiring 60–70 $	ext{in}^{2}$ per adult rat compared to ~12 $	ext{in}^{2}$ per adult mouse. The result is that a standard rat cage holds far fewer animals, and per-diem costs scale up accordingly.

Question 3

How do I handle aging studies with growing rats?

Accepted Answer

Plan for the highest weight class the rats will reach during the study, not the starting weight. A rat that starts at 250 g and ends at 550 g spends most of the study in the 400–500 g and over 500 g classes, so cage allocation should be based on the larger requirement. The calculator does not auto-track weight class transitions — verify with your colony management software or pre-allocate by final weight.

Question 4

What cage types does the calculator use?

Accepted Answer

The calculator includes three vendor-standard rat cages: small (~116 $	ext{in}^{2}$ usable, e.g. Tecniplast 1284L), medium (~142 $	ext{in}^{2}$, e.g. Tecniplast 1291H), and large (~162 $	ext{in}^{2}$, e.g. Tecniplast 2000P or double-deck cages). These are typical usable floor areas from manufacturer datasheets — confirm against the exact cage your facility uses, since usable floor area can differ from external footprint by 20% or more.

Question 5

Why does the cost calculation use a daily rate?

Accepted Answer

Most US academic vivariums charge a per-diem rate per cage per day, not per animal. The calculator multiplies (cages $	imes$ rate $	imes$ days) and converts to a monthly burn rate using 30.4375 days/month (the average across a year). If your facility charges per animal instead of per cage, divide the cage rate by your typical occupancy.

Rat Per-Diem Cost Calculator.

Calculator

Cohort & Housing

Cost & Density

Plan for the final weight, not the starting weight

Cage usable floor area ≠ external footprint

Rat per-diem dominates many study budgets

Solo housing requires enrichment justification

Method

Validated

How to cite

How to Cite

NIH Guide Table 3.3 — Rat Floor Area

Why Rat Housing Is Expensive

Frequently asked

Next steps

ConductColony — auto-track rat weight classes and cage assignments

Rat Cages & Housing

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