01
Pipe Size Calculator
Choose a nominal supply-pipe size without guessing.
| You enter | Expected flow, pipe material, and velocity limit |
|---|---|
| You receive | Recommended size, inside diameter, velocity, and pressure check |
Plan with the information you have
Plumbing Calculators
Choose the plumbing problem you are solving. Size a water-supply pipe from known flow, calculate water flow, set drain fall, estimate water-heater capacity, or turn a fixture list into plumbing demand. Each tool keeps its calculation separate and shows how the result was reached.
Start with what you know Compare practical options Check the assumptions
Choose a part of the system
System guide
Choosing a Pipe Size
A supply pipe needs enough inside diameter to carry peak flow without excessive velocity or pressure loss.
| How to choose | Start with design flow, then compare actual inside diameters at the velocity you want. |
|---|---|
| Also check | Long runs, fittings, available pressure, and elevation can require the next size up. |
Start with the question
Five Plumbing Calculation Paths
Each tool begins with different inputs and reports a separate result, method, and set of limits.
02
Water Flow Rate Calculator
Turn a bucket test or pipe data into a usable flow rate.
| You enter | Collected volume and time, or known pipe conditions |
|---|---|
| You receive | Water flow in GPM, L/min, and L/s |
03
Drain Pipe Slope Calculator
Plan a drain run with enough fall from end to end.
| You enter | Horizontal run, pipe diameter, and available drop |
|---|---|
| You receive | Required grade, fall per length, and total drop |
04
Water Heater Size Calculator
Match hot-water capacity to real peak usage.
| You enter | Simultaneous uses or busiest-hour demand and temperatures |
|---|---|
| You receive | Tank first-hour rating or tankless flow target |
05
Plumbing Fixture Calculator
Add a fixture schedule before sizing supply or drainage.
| You enter | Plumbing code basis, fixture types, and quantities |
|---|---|
| You receive | Water-supply and drainage fixture-unit totals |
Start with a real task
Typical Plumbing Jobs and Starting Inputs
Gather the information in the middle column before you calculate. It will make the result more useful and help you know what to check next.
| Typical job | Start by collecting | Use this tool first | Check after the result |
|---|---|---|---|
| Extend or replace a water-supply run | Design flow, pipe material, developed length, and available pressure if known | Pipe Size Calculator | Actual inside diameter, velocity, fittings, elevation, and pressure loss |
| Investigate weak flow at one fixture | A known container volume, fill time, and whether other fixtures were running | Water Flow Rate Calculator | Pressure, restrictions, valves, pipe condition, and simultaneous demand |
| Run a new horizontal drain | Horizontal developed length, pipe diameter, available vertical drop, and adopted code basis | Drain Pipe Slope Calculator | Uniform fall, cleanouts, fittings, and local drainage requirements |
| Choose a heater for a busy household period | Simultaneous hot-water uses, inlet-water temperature, and desired outlet temperature | Water Heater Size Calculator | First-hour rating, recovery, fuel or electrical capacity, and manufacturer data |
| Plan plumbing for a new fixture group | Fixture types, quantities, line role, and the adopted plumbing code | Plumbing Fixture Calculator | The accepted demand method before sizing supply piping or drainage |
Plumbing Calculator Methodology & Limits
These are planning and sizing aids. The adopted plumbing code, local amendments, site conditions and manufacturer requirements govern an installation. A result should be checked against the project’s actual pressure, demand and permitted sizing method; it is not a global statement of code compliance.
Practical answers
Plumbing Calculator FAQs
Use these answers to choose a starting point and understand what a result means.
Should I start with fixture units or water flow when sizing a supply pipe?
Use fixture units when you are starting with a fixture schedule and an accepted demand method. Use water flow when design GPM or L/min is already known or has been measured. Pipe sizing comes after design flow is established.
Is nominal pipe size the same as the inside diameter?
No. Nominal size is a trade name. The actual inside diameter changes with pipe material and wall thickness, and that actual bore is what affects velocity and pressure loss.
Can pressure alone tell me how much water flow I have?
No. Flow also depends on pipe diameter, developed length, fittings, elevation, valves, and how much water other fixtures are using at the same time.
How can I measure water flow with a bucket and stopwatch?
Collect water in a container with a known volume and time the fill. Divide the volume by the fill time, then convert to GPM, L/min, or L/s. Repeat the test at the same fixture for a more dependable result.
What should I check before relying on a calculator result?
Confirm the entered units, pipe material, actual dimensions, available pressure, fixture assumptions, and adopted local code. A calculator supports a decision; site conditions and project requirements still govern the installation.