How to use the continuity equation calculator
Find fluid speed in a pipe after a change in diameter. Enter diameter 1, speed 1, diameter 2 in the fields above; the speed 2, flow rate are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- D1 — Diameter 1 (cm)
- v1 — Speed 1 (m/s)
- D2 — Diameter 2 (cm)
Worked example
With diameter 1 = 5 cm, speed 1 = 2 m/s, diameter 2 = 2 cm, the calculator gives speed 2 ≈ 12.5 m/s; flow rate ≈ 3.926991 L/s.
Frequently asked questions
What is the formula for the continuity equation calculation?
Speed 2 (m/s) = v1 × (D1 / D2)^2. Flow rate (L/s) = v1 × π × (D1 / 100)^2 / 4 × 1000. Here D1 is diameter 1 (cm), v1 is speed 1 (m/s), D2 is diameter 2 (cm).
What inputs do I need for the continuity equation calculator?
You need diameter 1 in cm, speed 1 in m/s, diameter 2 in cm. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.