Flowbox: Plumber Toolkit

Flowbox is a professional toolkit for plumbers — job-site calculators covering drainage, venting, water supply, gas piping, and pipe fitting, all on-device with no account required.

PIPE FUNDAMENTALS
• Pipe Slope — solve rise, run, or grade against IPC minimums
• Pipe Offset — travel and run for 45°, 22.5°, 60°, and other fittings
• Flow Rate & Pressure Drop — Hazen-Williams friction loss for water pipe runs
• Pipe Volume — water capacity of a pipe segment from ID and length

DRAINAGE & VENTING
• Drain Sizing — minimum drain pipe size from fixture unit load (DFU)
• Vent Sizing — vent pipe diameter from DFU load and developed length
• Sump/Ejector Pump Sizing — total dynamic head and horsepower from inflow and lift
• Grease Trap Sizing — interceptor capacity from kitchen fixture flow rate

SUPPLY & GAS
• Water Supply Sizing — distribution pipe size from fixture unit demand (WSFU)
• Gas Pipe Sizing — pipe size from BTU load and length, longest-length method
• Water Heater Sizing — first hour rating or tankless GPM from peak demand
• Water Hammer Arrestor — PDI-WH201 size from branch fixture units
• Thermal Expansion — pipe growth and expansion loop size by material

WHY FLOWBOX
Pro unlock is a one-time purchase — no subscription, ever. No ads. No server required to use any calculator. Free tools (Pipe Slope, Drain Sizing, Pipe Volume) cover everyday use; Pro unlocks the full set. An optional Pro feature lets you sync your saved calculations and projects across your own devices via your own iCloud or Google Drive — off by default, and your data never touches our servers because we don't have any.

Flowbox is a reference tool for estimating — always verify pipe slope, drain and vent sizing, water supply sizing, and gas pipe sizing against your local plumbing code (IPC or UPC as adopted locally) and a licensed professional before cutting, sizing, or installing. Gas piping in particular carries real safety consequences if undersized or misrouted.