Calculation sequence
Step-by-step method
- Convert entered geometry and fluid properties to a consistent SI calculation basis.
- Calculate area, velocity, and Reynolds number.
- Calculate Darcy friction factor and apply Darcy–Weisbach pressure loss.
MechanicalAdvancedHydronic Piping
Darcy–Weisbach Pipe-Loss Calculator
Calculate liquid velocity, Reynolds number, Darcy friction factor, and straight-pipe pressure loss from actual fluid and pipe properties.
Why it matters: Darcy–Weisbach provides a general pressure-loss method when density, viscosity, roughness, and inside diameter are known.
Calculated result
Engineering evaluation
Straight-pipe pressure loss (ΔP)1.449 psi
- Fluid velocity (V)
- 5.208 ft/s
- Reynolds number (Re)
- 123,600 ratio
- Darcy friction factor (f)
- 0.02 ratio
- Friction head (Hf)
- 3.344 ft
Engineering interpretation
Calculated straight-pipe loss is 1.449 psi (3.344 ft of fluid head), at velocity 5.208 ft/s, Re 123600, and Darcy f 0.02028.
Important limitations
- Add fittings, valves, equipment, elevation, and static head separately. Verify fluid properties and pipe roughness at operating condition.
Engineering knowledge center
Understand the calculation—not just the answer
Governing relationships
A = πD²/4
V = Q/A
Re = ρVD/μ
f = 64/Re for laminar flow or f = 0.25/[log10(ε/(3.7D)+5.74/Re^0.9)]² for turbulent flow
ΔP = f(L/D)ρV²/2
Hf = ΔP/(ρg)
Current substitution
V = 5.208 ft/s; Re = 123600; f = 0.02028; ΔP = 1.449 psi.
Equation legend
Inputs and calculated quantities
- Q
- Liquid flow — gpm or L/s
- D
- Actual inside diameter — in. or mm
- L
- Straight pipe length — ft or m
- ρ
- Fluid density — lb/ft³ or kg/m³
- μ
- Dynamic viscosity — cP
- ε
- Absolute roughness — in. or mm
- ΔP
- Straight-pipe pressure loss — psi
- V
- Fluid velocity — ft/s
- Re
- Reynolds number — ratio
- f
- Darcy friction factor — ratio
- Hf
- Friction head — ft
Applications
How this calculation is used
Building design
Evaluate straight-pipe loss for water or glycol.
Construction
Check the impact of installed pipe size, schedule, and length.
Commissioning
Compare measured differential pressure with calculated straight-pipe loss.
Quality controls
Assumptions and limitations
Assumptions
- Entered values describe one stable operating condition and use consistent measurement boundaries.
- Fluid or air properties and geometric dimensions are representative of the evaluated system.
Limitations
- This is a preliminary evaluation and field-verification tool, not a final sizing or code-compliance determination.
- Manufacturer data, adopted codes, project criteria, and professional engineering review remain controlling.
Field use
Verification procedure
- Confirm the approved reference, measurement plane, and instrument calibration.
- Stabilize the system and record dimensions and operating data.
- Compare the calculated result with project documents and manufacturer data before disposition.
Common engineering mistakes
- Using outside dimensions rather than clear inside dimensions.
- Combining values from different loads, device positions, or measurement conditions.
Technical basis
References and source standards
- ASHRAE Handbook—FundamentalsCurrent handbook chapters covering duct design, fluid flow, heat transfer, insulation, and measurement; verify the licensed edition during professional review.
- U.S. Department of Energy—Improving Pumping System PerformanceFederal sourcebook for pumping-system flow, head, losses, controls, and energy relationships.
Engineering calculation disclaimer
These engineering tools are provided for educational, preliminary evaluation, field verification, and commissioning support. Results depend on the accuracy of user-entered information and the assumptions stated for each calculation. Every colored status and comparison is a screening indicator only; project criteria, contract requirements, applicable codes, manufacturer instructions, measurement uncertainty, and authorized engineering judgment govern. The tools do not replace project-specific engineering analysis or the judgment of a licensed professional engineer.
Read the full use and limitation statement