Hazen–Williams Head Loss (Water) Calculator

Advanced calculator for water pipelines using Hazen–Williams empirical relation with unit toggles. Switch between SI and US units with intelligent diameter conversions and presets. Select roughness classes for C presets and material-based typical ranges to guide. See velocity, head loss, slope, and pressure drop instantly computed. Export results to CSV and PDF for sharing.

Density auto-adjusts with temperature.
Higher C means smoother pipe; typical 100–160 for water.
Formula used

The head loss due to friction using the Hazen–Williams relation:

hf = 10.67 · L · Q1.852 / (C1.852 · D4.8704) with Q in m³/s, D and L in m, giving hf in meters.

In US feet-based units (Q in ft³/s, D and L in ft):

hf = 4.727 · L · Q1.852 / (C1.852 · D4.8704) giving hf in feet.

Common handy form for gpm‑inches per 100 ft:

hf,100ft = 4.52 · (Qgpm/C)1.852 / din4.871

How to use this calculator
  1. Select your unit system and set water temperature.
  2. Enter flow rate, pipe inside diameter, and pipe length with matching units.
  3. Choose a material preset or enter a custom C value.
  4. Click Calculate to show head loss, slope, velocity, and pressure drop.
  5. Use Add to table to record the current result.
  6. Export the results table to CSV or PDF for documentation.
Results history
# Q D L C hf (m) hf (ft) ΔP (kPa) V (m/s)
Example data
# Q (value) Q unit D (value) D unit L (value) L unit C T (°C)
120L/s200mm500m14020
22L/s50mm100m15020
3150gpm3in800ft13020
41000L/min100mm200m14520
50.5m3/s0.6m2000m12020
FAQs

Use Hazen–Williams for water in turbulent flow and typical municipal or building services, when only C is known. Use Darcy–Weisbach when fluid properties and friction factors are available.

New plastics: ~150. New steel or cement‑lined ductile iron: ~140. Galvanized iron: ~120. Aged cast iron: ~100. Choose conservatively for aging systems.

Hazen–Williams does not explicitly include viscosity. We use temperature only to compute water density for converting head loss to pressure drop.

No. The relation is empirical for water. For other fluids, switch to Darcy–Weisbach with appropriate viscosity and density.

Practical engineering use spans roughly 50–3000 mm diameters, and velocities about 0.3–3 m/s for distribution systems. Outside these ranges, check validity.

Model minor losses by converting each fitting to an equivalent length, add to straight length, or use loss coefficients (K) and convert to head.

Different unit conventions and rounding of exponents (4.87 vs 4.8704) or constants (10.67 vs 10.68) cause small variations. Ensure units and C are consistent.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.