Free plumbing calculators — pipe sizing, gas lines, offsets & job estimates
PlumbCalc Pro is a free plumbing calculator suite for contractors and DIY homeowners. Size a pipe by flow rate, calculate a gas line, work out a 45° offset, or estimate materials, labor, and permit fees — instantly in your browser, no signup required. Every calculator gives you a clear number you can take straight to the job.
Jump to a tool: pipe diameter, pipe sizing, gas line sizing, water flow rate, or pipe volume.
Pipe sizing & diameter calculator
Enter your flow rate in GPM and the run length, and the pipe diameter calculator returns the recommended diameter with friction loss, so you avoid undersizing a line or paying for an oversized one. The pipe sizing calculator handles the full run. These are the everyday numbers a plumbing calculator should give you in seconds instead of a chart lookup — the same flow formulas documented by references like the Engineering ToolBox.
Gas line sizing calculator
The gas line sizing calculator sizes natural-gas piping to NFPA 54 so each appliance gets the BTU it needs. There is also a worked natural-gas pipe sizing example that walks through a real 90-foot run step by step — handy when you want to see the method, not just the answer.
Water flow & pipe volume
Need the other direction? The water flow rate calculator turns pipe size and pressure into GPM, and the pipe volume calculator tells you how much water a run holds — useful for purging, dosing, and fill times.
Materials, labor & permit estimates
PlumbCalc Pro is more than a pipe calculator. Estimate material takeoffs, labor hours, markup, and permit fees so your bid reflects the real cost of the job. Save any calculation to Projects to keep a job organized and reuse the numbers later.
Built for plumbers and DIYers
Whether you run a shop or you are sweating your first copper joint at home, PlumbCalc Pro gives you a plumbing calculator you can trust for a fast, defensible number. It is free to use, works on your phone out on the truck, and never asks for a download.
Plumbing calculator — frequently asked questions
What pipe size do I need for a given GPM?
Enter your flow rate in GPM and run length into the pipe diameter calculator and it returns the recommended diameter and friction loss. Larger flows and longer runs need larger pipe.
How do I calculate a gas line size?
Use the gas line sizing calculator: enter the appliance BTU load and pipe length, and it sizes the pipe to NFPA 54 so each appliance gets enough gas.
Is PlumbCalc Pro free?
Yes — the core plumbing calculators are free in your browser with no signup. An optional one-time PRO purchase unlocks advanced calculators.
Are the results code-compliant?
Results are estimates for guidance based on standard formulas and NFPA 54. Always confirm against your local plumbing code and a licensed inspection before final work.