THC/CBD Ratio Calculator
Enter the THC and CBD percentages (or mg) from your cannabis product label to calculate the ratio and understand its likely effects profile.
Formulas Used
THC : CBD Ratio — Divide both values by their Greatest Common Divisor (GCD) to express the simplest whole-number ratio:
Ratio = (THC / GCD) : (CBD / GCD)
CBD Modulation Index — The proportion of total cannabinoids that is CBD:
Modulation Index (%) = CBD / (THC + CBD) × 100
Estimated Effective THC — A simplified model (based on Russo's entourage effect research) estimating how CBD attenuates perceived THC potency:
Effective THC = THC × (1 − 0.5 × (CBD / (THC + CBD)))
The 0.5 coefficient reflects that CBD partially (not fully) antagonises THC at CB1 receptors.
Assumptions & References
- THC and CBD values are assumed to be as-labelled (post-decarboxylation for % values, or as measured for mg values).
- Dominance thresholds (e.g., ≥10:1 = High THC Dominant) are based on commonly used clinical and dispensary classification frameworks.
- The Effective THC formula is a simplified approximation. CBD's modulation of THC is dose-dependent and varies by individual; this is not a clinical dosing tool.
- Russo, E.B. (2011). Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects. British Journal of Pharmacology, 163(7), 1344–1364.
- MacCallum, C.A. & Russo, E.B. (2018). Practical considerations in medical cannabis administration and dosing. European Journal of Internal Medicine, 49, 12–19.
- This calculator is for informational purposes only and does not constitute medical advice.