Size a water-supply pipe from either an entered friction allowance or a complete pressure budget, then check a candidate actual inside diameter.
Trades & Professional Tools · Plumbing
Enter your project measurements
Measured inputs · visitor-entered product and design assumptions
1EnterProvide the known values
2CalculateResults update automatically
3VerifyReview the details and units
Try an example
Measure using one consistent system. Product coverage, density, resistance, waste, and safety assumptions must come from the actual product data or project specification. Values stay in this browser.
Trade calculator result
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Translate a pressure allowance and design flow into a minimum actual inside diameter, then check a candidate bore.
At a glance
See the relationship
Design water flowStraight developed length (m or ft)Equivalent fitting length (m or ft, optional)Hazen–Williams C factor
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Water Supply Pipe Sizing resultThe calculator connects the entered project values above to the result below. Change one input at a time to see which assumption drives the outcome.
The relationship
The formula used here
Available friction pressure = supply − required residual − elevation pressure − equipment loss; convert that budget to head, solve Hazen–Williams diameter, and compare the entered candidate against both friction and velocity constraints.
This is the relationship applied to your inputs. Read the outputs together rather than treating one displayed number as a complete plumbing decision.
Field reading
Use the result as a next check
Enter real project values
Use site measurements, manufacturer information, and the same unit basis throughout.
Read the full result
Enter all pressure-budget losses and use a candidate's actual inside diameter, not its nominal size.
Keep the boundary clear
It is a planning comparison, not pipe selection, code sizing, or an approved hydraulic design.
Quick guide
How to use this calculator
Choose the calculation mode or measurement system that matches the values you actually have.
Enter measured project dimensions and use product-specific coverage, density, yield, resistance, or waste data where requested.
Review the intermediate results before ordering material or applying the result on site.
Calculation method
Calculation method
Available friction pressure = supply − required residual − elevation pressure − equipment loss; convert that budget to head, solve Hazen–Williams diameter, and compare the entered candidate against both friction and velocity constraints.
The calculator preserves full internal precision and rounds only displayed results. Quantity outputs round up when whole purchasable pieces are required.
Worked example
Worked example
A 30 m run carrying 30 L/min with C = 140 and 3 m allowed friction needs about 22.1 mm inside diameter.
Available friction pressure = supply − required residual − elevation pressure − equipment loss; convert that budget to head, solve Hazen–Williams diameter, and compare the entered candidate against both friction and velocity constraints.
Supported inputs
Precision and limits
Water-property assumptions
Where a calculator does not request fluid properties, it models water at 998.2 kg/m³ density and 4,186 J/(kg·K) specific heat. Temperature, pressure, dissolved content, or a different fluid can change real results.
Planning scope
This calculator supports measurement, estimating, and scenario planning. It does not inspect a site, select a product, certify a design, or replace drawings, specifications, manufacturer instructions, local codes, permits, or a qualified trade professional.
Measured and product-specific inputs
Nominal dimensions can differ from actual dimensions. Verify inside pipe diameters, actual lumber sizes, product coverage, bag yield, material density, conductor resistance, waste, and packaging against the materials used on the project.
Safety and regulatory limits
Electrical, HVAC, structural, excavation, roofing, pressure, lifting, and life-safety work may require jurisdiction-specific calculations and professional approval. Do not use a generic planning result as a code-compliance or safety determination.
Precision and privacy
Inputs accept bounded plain decimals. Calculations remain in this browser and raw entered project values are not submitted to 365CALCS.COM.
