Common Questions About Faucet Sizing & Flow
How do I calculate water flow based on pipe/hole size?
To calculate flow rate, you need the diameter of the opening (orifice) and the water pressure. The physics formula used is Q = Cd × A × √(2gh) or simplified for pressure as Q = 29.84 × Cd × d² × √P (for GPM with diameter in inches). This calculator automates that complex math for you.
How many GPM flows through a 1/2 inch hole?
It depends heavily on pressure. At a standard household pressure of 40 PSI, a 1/2-inch opening can discharge approximately 28 to 30 GPM (assuming a discharge coefficient of 0.62). However, connected plumbing usually restricts this flow significantly due to friction.
What is the standard size for a faucet opening?
Most residential supply lines use 3/8-inch or 1/2-inch fittings. However, the actual aerator (the mesh tip where water exits) restricts flow to meet federal conservation standards, usually capping it at 2.2 GPM for kitchens and 1.5 GPM for bathrooms.
Does doubling the hole size double the flow rate?
No, it actually quadruples the flow rate. Since the area of a circle is calculated using the square of the radius (A = πr²), doubling the diameter increases the area by a factor of four, allowing four times as much water to pass through at the same pressure.
What is the discharge coefficient (Cd)?
The discharge coefficient (Cd) represents how "efficient" the hole is. A perfect nozzle has a Cd of 1.0. A standard sharp-edged hole (like a drilled hole in a tank) creates turbulence, reducing the Cd to about 0.60 - 0.62. This calculator defaults to 0.62 for realistic results.