Plumbing Pipe Diameter Calculator
Find the minimum Schedule 40 pipe size for your target flow, before you commit to a bulkhead size you can't change later.
Your Line
Minimum pipe diameter
1.5 in
size up one pipe size for a gravity drain, this is a hobby safety margin, not the pipe's absolute limit
| Pipe (Sch 40) | Gravity drain max | Pressurized max |
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Why gravity drain numbers vary: unlike a pressurized line, gravity/siphon flow depends heavily on head pressure, drop length, and overflow design (Durso, Herbie, Bean Animal). Treat the gravity-drain figures as a practical ceiling for noise and siphon reliability, not the pipe's true physical limit, and always oversize the drain relative to your return pump's rated GPH.