Diastolic-to-Systolic Ratio Calculator

How it is calculated

Both readings are in mmHg, systolic (upper number) first. The tool gives three results. The ratio is DBP ÷ SBP, shown with two decimals. Pulse pressure is SBP − DBP. Mean arterial pressure uses the common estimate MAP = DBP + (SBP − DBP) ÷ 3. Pulse pressure and MAP are rounded to whole mmHg. Readings outside physical limits show no result: systolic must be 50 to 300, diastolic 20 to 200, and diastolic must be lower than systolic (equal values are rejected). The MAP formula is an approximation that does not use heart rate and is not a substitute for a measured arterial line value. For education only.

Common mistakes

• Entering the readings in the wrong order. Systolic is the larger number. If the diastolic field is higher or equal, the tool gives no result at all.
• Treating MAP as the plain average of the two numbers. The formula is diastolic plus one third of the pulse pressure, so diastolic counts twice as much and 138/84 gives 102, not 111.
• Entering a pulse rate or a kPa value in place of mmHg. A kPa reading such as 18/11 falls below the accepted range and shows nothing, and a pulse rate would pass as a pressure if it happened to fit the range.
• Reading the ratio as a percentage. It is a fraction, so 0.61 means diastolic is 61 % of systolic.
• Typing a value outside the accepted ranges, such as 900 over 80, and expecting a calculation. Systolic above 300 or diastolic under 20 shows no result.