Wells & water/ CALCULATOR
Convert flow and internal pipe diameter into water velocity.
FROM ESTIMATE TO ACTION
Enter flow in L/min and internal diameter in mm: 20 and 25, not 0.025 in the diameter field. Use the product bore, not DN or outside diameter; do not open a pressurised pipe to measure it. A measured 10 L in 30 s is 20 L/min at that operating condition, not proof of peak demand. For a common supply section, use the combined flow of outlets operating together, not one branch alone.
At 20 L/min and 25 mm, the area is about 491 mm² and the cross-section average velocity is 0.68 m/s. Doubling flow to 40 L/min doubles velocity to 1.36 m/s. Keeping 20 L/min but halving bore to 12.5 mm makes velocity four times as high: 2.72 m/s. These are comparisons, not recommended speeds. In a series route with no branches or leaks, the same flow passes through each section; calculate its own diameter separately.
The two inputs do not determine the flow a pump will actually deliver. This model assumes steady flow in a completely full circular pipe; it does not apply directly to partly full drains. It does not calculate pressure loss, water hammer, noise or an allowable velocity. Pipe length, fittings, material and operating conditions need separate checks. Neither a low nor a high displayed speed alone establishes that the installation is suitable.