LogP Partition Calculator
The partition coefficient P is the ratio of a compound's equilibrium concentration in 1-octanol to its concentration in water. LogP = log10(P) = log10([organic]/[aqueous]). It is the most widely used measure of lipophilicity in medicinal chemistry and environmental science. A logP of 2 means the compound is 100 times more concentrated in octanol than in water. Lipinski's Rule of Five states that an orally active drug typically has logP at most 5. Enter the measured concentrations in the organic (octanol) and aqueous (water) phases to calculate logP and P directly.
LogP formula
P = [organic] / [aqueous]
logP = log10(P)
Both concentrations must be in the same units. P is the partition coefficient and logP is its base-10 logarithm. Positive logP means lipophilic (prefers organic phase). Negative logP means hydrophilic (prefers water). The standard reference system is 1-octanol / water (OECD guideline 107).
LogP reference values for common compounds
- Ethanol: logP = -0.31 (hydrophilic).
- Aspirin (acetylsalicylic acid): logP = 1.19.
- Ibuprofen: logP = 3.97 (lipophilic oral drug).
- Diazepam (Valium): logP = 2.82 (CNS active).
- DDT (dichlorodiphenyltrichloroethane): logP = 6.91 (highly lipophilic, bioaccumulates).
LogP: frequently asked questions
What is logP?
LogP is the base-10 logarithm of the ratio of a compound's concentration in 1-octanol to its concentration in water at equilibrium: logP = log10([octanol]/[water]). It quantifies lipophilicity. Positive logP means the compound prefers the organic phase (lipophilic); negative logP means it prefers water (hydrophilic).
Why is logP important in drug design?
LogP strongly influences absorption, distribution, metabolism, excretion, and toxicity (ADMET). Lipinski's Rule of Five requires logP at most 5 for orally bioavailable drugs. Compounds with high logP tend to cross cell membranes but may be poorly soluble in water. Low logP compounds are more water-soluble but may not penetrate membranes.
What is the difference between logP and logD?
LogP is measured for the neutral (unionized) form of a molecule. LogD is the distribution coefficient at a specific pH and accounts for the ionization state of the compound. For acids and bases, logD varies with pH because the ionized form has lower logP than the neutral form.
How is logP measured experimentally?
The standard shake-flask method equilibrates the compound between octanol and water, then measures concentration in both phases (e.g., by UV absorbance). HPLC-based methods use correlations between retention time and logP. The OECD guideline 107 describes the shake-flask method for regulatory purposes.
What is a typical logP range for drug molecules?
Most approved oral drugs have logP between -1 and 5. Central nervous system drugs (cross blood-brain barrier) often have logP 1 to 3. Lipinski Rule of Five: logP at most 5. Very lipophilic compounds (logP above 5) tend to have poor solubility and may accumulate in fatty tissue.
Official sources
- OECD: OECD Test Guideline 107: Partition Coefficient (n-octanol/water).
- IUPAC: IUPAC Quantities, Units and Symbols in Physical Chemistry.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.