Pipe Pressure Drop Hazen Williams
Calculator
Results
- Head loss (m of water)
- 5.902083
- Pressure drop (kPa)
- 57.879664
- Pressure drop (bar)
- 0.578796
- Head loss per 100 m (m)
- 11.804166
HVAC and plumbing results
| Head loss (m of water) | 5.902083 |
| Pressure drop (kPa) | 57.879664 |
| Pressure drop (bar) | 0.578796 |
| Head loss per 100 m (m) | 11.804166 |
formula-map diagram
- Head loss (m of water)
- 5.902083
- Pressure drop (kPa)
- 57.879664
- Pressure drop (bar)
- 0.578796
- Head loss per 100 m (m)
- 11.804166
HVAC and plumbing relationship
Formula
hf = 10.67 × L × Q^1.852 ÷ (C^1.852 × D^4.87)= 5.9020832051729
Note
This is a simplified model: it applies a standard engineering formula to the numbers you entered. Conversions between BTU/h and kW use the exact factor 1 kW = 3412.142 BTU/h, but every sizing figure is an estimate. Air conditioner sizing uses the common 20 BTU/h per square foot rule of thumb, not a room-by-room load calculation, and it ignores insulation, glazing, orientation, ceiling height, infiltration and local climate. Heating loads use a single volumetric heat-loss factor in W/m³·K rather than a fabric-by-fabric U-value calculation. Air properties are fixed at 1.2 kg/m³ and water at 1000 kg/m³ and 4186 J/kg·K, with no correction for temperature, altitude or glycol. Duct and pipe results use the ideal continuity equation and ignore fittings, bends, roughness and system effect unless you enter those losses yourself. The Hazen-Williams equation is valid only for water in full turbulent flow at ordinary temperatures. Water hammer uses the Joukowsky surge, an upper bound for instant closure. Tank drainage assumes a prismatic tank and steady free discharge. Hot water recovery and condensate figures ignore standing losses and coil bypass. Size real systems with a proper heat-loss survey and have the work checked by a qualified HVAC or plumbing professional.
More in HVAC and plumbing
See all →Frequently asked questions
What is the Hazen-Williams equation used for?+
It estimates the friction-caused pressure (or head) loss as water flows through a pipe, based on the pipe's diameter, length, flow rate, and a roughness coefficient specific to the pipe material. It's widely used in water supply and plumbing design because it's simpler to apply than more rigorous fluid dynamics equations.
What does the roughness coefficient (C-factor) represent?+
It quantifies how smooth or rough the pipe's interior surface is: smoother materials like new PVC or copper have higher C-values (150+) and less friction loss, while rougher or corroded materials like older cast iron have lower C-values and more friction loss for the same flow.
Why does pipe age affect the pressure drop calculation?+
Mineral scale buildup and corrosion roughen a pipe's interior over time, lowering its effective C-factor and increasing friction loss compared to when it was new — this is why older piping systems often show reduced flow and pressure even without any leaks.
Is the Hazen-Williams equation accurate for all fluids?+
No, it was developed specifically for water at typical ambient temperatures and is not accurate for other fluids or for water at temperature extremes; the Darcy-Weisbach equation is the more universally applicable (but more complex) alternative.
How much does flow rate affect pressure drop compared to pipe diameter?+
Pressure drop increases roughly with flow rate to the power of 1.85 but decreases with diameter to the power of about 4.87, so increasing pipe diameter has a dramatically larger effect on reducing pressure drop than reducing flow rate by the same proportion.