Calculate blood flow rate from volume and time, or from mean velocity and vessel diameter (Q = v × A), and solve for volume, time, velocity or diameter.
Measurement notice: This page provides arithmetic and circular-vessel estimates only. It does not calculate IV drip, transfusion, medication infusion, or prescribed pump settings.
Blood Flow Rate Formulas
Volumetric flow rate is volume divided by elapsed time. When a vessel is modeled as circular, flow rate can also be estimated from time-averaged velocity and cross-sectional area.
- Q is volumetric flow rate.
- V is volume.
- t is elapsed time.
- vmean is mean velocity across the lumen, not peak velocity.
- d is the modeled circular internal diameter.
Measurement Limits
The velocity-and-diameter mode is a geometric estimate. Real vessels may not be perfectly circular, diameter can change during the cardiac cycle, and ultrasound flow calculations depend strongly on sampling location, angle correction, and use of a suitable time-averaged velocity. A small diameter error is squared when area is calculated.
Use a representative time-averaged mean velocity measured at the same vessel location and cardiac cycle as the diameter; the estimate assumes a circular lumen, and diameter error is squared in area. Do not substitute peak systolic velocity for time-averaged mean velocity unless a validated protocol specifically calls for it.
Examples
If 500 mL passes a point in 2 minutes, the arithmetic flow rate is 250 mL/min.
For a modeled 5 mm circular vessel with mean velocity 20 cm/s, the area is about 0.19635 cm² and the estimated flow is about 3.927 mL/s.
What This Calculator Does Not Do
This page does not calculate IV drip rate, tubing drop factor, transfusion rate, medication infusion, or a prescribed pump setting. Use the dedicated infusion tools and follow clinician orders and local protocols for those tasks.
Frequently Asked Questions
Is blood flow rate the same as blood flow velocity?
No. Flow rate is volume per unit time, while velocity is distance per unit time.
Does this result diagnose poor circulation?
No. It is an arithmetic or geometric estimate and must be interpreted with the measurement method and clinical context.
