Convert mouse, rat, and human doses using the Reagan-Shaw et al. (2008) FASEB J body-surface-area method. Computes human equivalent doses (HED) with canonical Km factors and cross-species comparison tables.
Try it out
Load example allometric dose scaling calculator data to see the full workflow
Defaults: mouse 25 g, rat 250 g, human 70000 g.
| Species | Weight | BSA | mg/kg | Total dose |
|---|---|---|---|---|
| mouse | 25 g | 0.0083 m² | 100.00 | 2.500 mg |
| rat | 250 g | 0.0417 m² | 50.00 | 12.500 mg |
| human | 70000 g | 1.8919 m² | 8.11 | 567.568 mg |
When to use
Do not use for
A 100 mg/kg mouse dose is NOT a 100 mg/kg human dose. The BSA correction gives ~8.1 mg/kg HED. Skipping this step is a common reason early human trials see unexpected toxicity.
Rats are larger and have a higher Km (6 vs 3 for mouse), so the correction is less aggressive. A 50 mg/kg rat dose translates to ~8.1 mg/kg HED — coincidentally the same as a 100 mg/kg mouse dose.
The method works when drug clearance is proportional to BSA across species. For drugs with saturable metabolism, target-mediated disposition, or species-specific metabolism, BSA scaling can be off by 10× or more.
The FDA Guidance recommends BSA scaling as the *starting* point for the maximum recommended starting dose (MRSD). The actual MRSD is then divided by a 10× safety factor. This calculator gives you the BSA-scaled HED — apply your own safety factor for clinical use.
BSA () = body_weight_kg / Km_species, where Km is the canonical Reagan-Shaw factor (mouse 3, rat 6, human 37). HED (mg/kg) = animal_dose (Km_animal / Km_human). The calculator generalizes this to any source/target pair in {mouse, rat, human} via Dose_target = Dose_source (Km_source / Km_target).
Last validated 2026-04-06. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Allometric Dose Scaling Calculator (v0.88.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/allometric-dose-scaling-calculator
Reagan-Shaw S, Nihal M, Ahmad N. Dose translation from animal to human studies revisited. FASEB J. 2008;22(3):659-661.
Nair AB, Jacob S. A simple practice guide for dose conversion between animals and human. J Basic Clin Pharm. 2016;7(2):27-31.
U.S. Food and Drug Administration. Guidance for Industry: Estimating the Maximum Safe Starting Dose in Initial Clinical Trials for Therapeutics in Adult Healthy Volunteers. CDER; 2005.
Reagan-Shaw, Nihal & Ahmad (2008) revisited the FDA Guidance for Industry on Estimating the Maximum Safe Starting Dose in clinical trials. The core insight is that drug clearance scales with body surface area, not body weight, across species.
For each species, Km = body_weight_kg / body_surface_area_m². This ratio is approximately constant within a species and reflects the fact that smaller animals have a much larger surface-to-volume ratio than larger animals.
HED (mg/kg) = animal_dose (mg/kg) (animal_Km / human_Km).
For mouse → human: HED = mouse_dose (3/37) mouse_dose 0.081. For rat → human: HED = rat_dose (6/37) rat_dose 0.162.
This calculator generalizes the formula to any pair of species in {mouse, rat, human}.
BSA scaling is a *starting point*, not a substitute for proper pharmacokinetic modeling. Conditions under which the method underestimates or overestimates the true HED:
Drugs cleared by saturable enzymes (e.g. high-affinity CYP3A substrates near Vmax) do not scale linearly with BSA. The mouse may clear the drug efficiently while the human is enzyme-saturated at the BSA-equivalent dose.
For monoclonal antibodies and other biologics, clearance is dominated by target binding and internalization. BSA scaling does not capture this — use receptor occupancy modeling instead.
Some CYP isoforms (CYP2D6, CYP2C19) have very different activity profiles between rodents and humans. A drug that is 90% cleared by CYP2D6 in humans may be cleared by an unrelated isoform in mice.
If the parent compound is a prodrug, BSA scaling on the parent dose can dramatically misestimate the active metabolite exposure. Always verify with PK data when active metabolites are involved.
Use BSA scaling for: (1) initial cohort sizing, (2) IACUC dose justification, (3) sanity-checking published doses, (4) FDA IND HED estimation per the 2005 Guidance for Industry. Do NOT use it as the final dose for a clinical trial without empirical PK data.
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