HED Calculator | Tools Hub

Dose Translation

Calculate Human Equivalent Dose (HED) from Animal NOAEL.

Source Species

Source Weight (kg)

Target Species

Target Weight (kg)

Source K_m Factor

Target K_m Factor

Source Dose / NOAEL

Calculate MRSD (Apply 10x Safety Factor)

Force Standard K_m (Ignore Weight Deviation)

Decimals:

Normalized Input (Source)

0 mg/kg

Target Equivalent Dose

0 mg/kg

Total Target Dose

0 mg

Math Breakdown

Enter values to see calculation...

Engineering & Scientific Notes

Source: Calculations follow the FDA's "Guidance for Industry: Estimating the Maximum Safe Starting Dose in Initial Clinical Trials..." (July 2005) Link.

Definitions:

NOAEL: No Observed Adverse Effect Level. Highest dose with no significant adverse effect.
HED: Human Equivalent Dose. Scaled via BSA (mg/m²).
MRSD: Max Recommended Starting Dose. Typically HED / 10.
K_m: Factor for converting mg/kg to mg/m². Equation: K_m = Weight (kg) / BSA (m²).

Note on Power Law: The formula W^0.33 is derived from the BSA relationship. Mathematically, 100/K × W^0.33 approximates the K_m factor when direct BSA data is missing.

Liability Waiver

FOR RESEARCH USE ONLY. This tool is intended strictly for theoretical dose estimation in preclinical research contexts. It is NOT for clinical use.

PERSONAL USE PROHIBITED. Do not use this tool to calculate doses for self-medication, "biohacking," or personal supplementation. Metabolism varies significantly between individuals and species. Ingesting substances based on these calculations can lead to severe injury or death.

LIMITATION OF LIABILITY. The creators assume NO LIABILITY for errors or outcomes. Users must validate all calculations against primary literature.

CONSULT A PROFESSIONAL. Always consult a licensed physician before taking any medication. This tool does not account for half-life, receptor affinity, or toxicity.

1. Standard Conversion (Appendix B)

When animal weights are within the standard FDA "working range", the conversion uses fixed K_m factors:

HED (mg/kg) = Animal Dose (mg/kg) × (Animal K_m / Human K_m)

2. K_m Factor Derivation

The K_m factor represents the ratio of body weight to body surface area. It is calculated as:

K_m = Weight (kg) / BSA (m²)

3. Reference Values (Table 3)

Species	Ref Weight	Range (kg)	BSA (m²)	K_m

4. Dynamic Conversion (Power Formula)

If an animal's weight falls outside the standard range, the calculator auto-switches to the Power Formula to maintain accuracy:

HED = Animal Dose × (W_animal / W_human)^0.33

5. BSA Estimation Logic

The tool estimates Body Surface Area (BSA) using the inverse of the K_m definition: BSA = Weight / K_m. By calculating the theoretical K_m first (using allometry), we derive a BSA that accurately reflects the animal's geometry (BSA ∝ Weight^0.67), rather than assuming a fixed ratio.

Compare how K_m shifts when you assume Body Surface Area (BSA) is fixed vs. when it scales allometrically.

Base Species

Input Weight (kg)

Est. BSA (m²) (?)

I acknowledge that calculating theoretical K_m values deviates from standard FDA guidance tables and is for novelty/research exploration only.

Why Linear Scaling Fails (The Square-Cube Law)

In biology, scaling an animal's weight linearly does not scale its surface area linearly. This is known as the Square-Cube Law:

Volume (Weight) increases by the cube of length (L³).
Surface Area increases by the square of length (L²).

Therefore, Surface Area is proportional to Weight raised to the power of 2/3 (or 0.67).

The Error: The "Linear K_m" calculation assumes Surface Area grows 1:1 with Weight. This underestimates the K_m factor for larger animals, leading to potentially dangerous overdoses when scaling from small to large species.