Cholesterol Ratio Calculator
Turn your cholesterol panel (mg/dL or mmol/L) into the ratios doctors watch — total-to-HDL, LDL-to-HDL and triglyceride-to-HDL — plus non-HDL cholesterol, the atherogenic index of plasma, an LDL estimate when LDL was not measured, and the category of every value.
How it works
Total-to-HDL = total ÷ HDL · LDL-to-HDL = LDL ÷ HDL · TG-to-HDL = triglycerides ÷ HDL · Non-HDL = total − HDL · AIP = log₁₀(TG ÷ HDL), both in mmol/L · Friedewald LDL = total − HDL − TG ÷ 5 · NIH (Sampson) LDL = TC/0.948 − HDL/0.971 − (TG/8.56 + TG × non-HDL/2140 − TG²/16100) − 9.44 (all in mg/dL; 1 mmol/L = 38.67 mg/dL for cholesterol and 88.57 mg/dL for triglycerides)
Cholesterol ratios put your panel into context better than any single number. The total-to-HDL ratio (also called the Castelli index) divides all your cholesterol by the protective HDL fraction, so a high HDL pulls it down; under 3.5 is considered ideal, and above 5 for men or 4.5 for women goes with higher risk. The LDL-to-HDL ratio compares the harmful and protective particles directly, and the triglyceride-to-HDL ratio is a rough marker of insulin resistance and small, dense LDL. Enter values in mg/dL or mmol/L (each field has its own unit menu) and the calculator also shows non-HDL cholesterol (everything except HDL, which many guidelines now use as a target), the atherogenic index of plasma, the category of each value under the US NCEP ATP III scheme and the share of your total carried by HDL, LDL and the rest. If your report has no LDL, choose an estimate: the classic Friedewald equation, or the newer NIH (Sampson) equation, which stays accurate with higher triglycerides and low LDL. Ratios are one useful lens, but doctors judge them alongside the absolute LDL or non-HDL number and your overall risk profile.
Worked example
With total cholesterol 200 mg/dL and HDL 50 mg/dL, total-to-HDL = 200 ÷ 50 = 4.0, in the moderate band. Adding LDL 120 gives an LDL-to-HDL of 2.4, and triglycerides 150 give a TG-to-HDL of 3.0. Non-HDL cholesterol is 200 − 50 = 150 mg/dL (3.88 mmol/L), and the atherogenic index of plasma is log₁₀(1.69 ÷ 1.29) ≈ 0.12, intermediate. Without a measured LDL, Friedewald estimates 200 − 50 − 150 ÷ 5 = 120 mg/dL and the NIH equation about 123 mg/dL. The same panel in mmol/L is total 5.17, HDL 1.29, LDL 3.10 and triglycerides 1.69.
Sources: American Heart Association — Cholesterol · NHLBI — ATP III cholesterol guidelines at a glance (lipid categories) · Sampson M et al. (2020), A new equation for calculation of LDL-C in patients with normolipidemia and/or hypertriglyceridemia, JAMA Cardiology · Millán J et al. (2009), Lipoprotein ratios: physiological significance and clinical usefulness in cardiovascular prevention, Vasc Health Risk Manag 5:757–765 · Dobiášová M (2004), Atherogenic index of plasma [log(triglycerides/HDL-cholesterol)]: theoretical and practical implications, Clin Chem
Frequently asked questions
What is a good cholesterol ratio?
For total-to-HDL, below 3.5 is often called ideal; above 5 in men or 4.5 in women goes with higher risk. For LDL-to-HDL, below 2 is very good and above 3.5 (men) or 3.0 (women) is high. A triglyceride-to-HDL ratio below 2 (with mg/dL values) is favourable, and 3 or more often goes with insulin resistance.
Can I enter my results in mmol/L?
Yes. Each field has a unit menu, so choose mmol/L next to the values that your lab reports in mmol/L. Ratios of cholesterol values are the same in either unit. The triglyceride-to-HDL ratio is not, because triglycerides convert with a different factor, so both versions are shown.
My report has no LDL. What should I choose?
Choose an estimate. The Friedewald equation (total − HDL − triglycerides ÷ 5) is what most labs used for decades but is not valid with triglycerides of 400 mg/dL or more. The NIH (Sampson) equation, published in 2020, is more accurate when triglycerides are high or LDL is low, and works up to 800 mg/dL.
What is non-HDL cholesterol?
It is total cholesterol minus HDL: all the cholesterol carried by particles that can build up in artery walls, including LDL and the triglyceride-rich remnants. It does not need a fasting sample and is used as a treatment target in US and European guidelines. Below 130 mg/dL (3.4 mmol/L) is desirable for most people.
Is the ratio more important than LDL?
They answer different questions. Ratios summarise the balance of your panel, while the absolute LDL (or non-HDL) level is the main target that treatment guidelines act on. Look at both rather than relying on either alone.
Related calculators
Educational estimate, not medical advice — for clinical decisions consult a healthcare professional.