The cholesterol ratio compares total cholesterol to HDL cholesterol (total cholesterol ÷ HDL). Because HDL is cardioprotective while total cholesterol includes all lipoprotein particles, this ratio captures the balance between atherogenic and protective cholesterol in a single number.

A cholesterol ratio below 4.0 is generally considered low risk; above 5.0 indicates elevated cardiovascular risk; above 6.0 indicates high risk. The ratio is useful because it incorporates HDL — meaning a high total cholesterol with very high HDL may actually carry low risk, while a borderline total cholesterol with very low HDL may carry significant risk. Australian cardiovascular guidelines use this ratio alongside absolute lipid values for risk stratification.