Head Loss Calculator
Head loss tells you how much energy (expressed in meters of fluid) a pipe system consumes due to friction. This is the number you need to select a pump, check if gravity flow is feasible, or evaluate pipe system efficiency. Get the friction factor first from the Moody Chart Calculator, then calculate head loss here.
Calculate Friction Head Loss
Results
Head Loss vs Pressure Drop - What's the Difference?
Both describe the same energy loss, just in different units. Pressure drop (ΔP) is in Pascals - useful for engineers working with gauges and instrumentation. Head loss (h_f) is in meters of fluid - useful when working with pump curves, which are almost always plotted in meters (or feet) of head.
They're related by: h_f = ΔP / (ρ × g). For water, ΔP of 1000
Pa equals about 0.102 m of head.
The Formula Explained
h_f = f × (L/D) × V² / (2g) - h_f - friction head loss (m)
- f - Darcy friction factor (from Moody Chart)
- L - pipe length (m)
- D - pipe internal diameter (m)
- V - average flow velocity (m/s)
- g - gravitational acceleration = 9.81 m/s²
Worked Example
Water flows at 1.5 m/s through a 150 mm diameter, 200 m long commercial steel pipe. Friction factor from the Moody Chart: f = 0.018.
h_f = f × (L/D) × V² / (2g)
h_f = 0.018 × (200 / 0.15) × (1.5²) / (2 × 9.81)
h_f = 0.018 × 1333.3 × 2.25 / 19.62
h_f = 0.018 × 1333.3 × 0.1147
h_f ≈ 2.76 m
This means the pump must provide at least 2.76 m of additional head just to overcome friction in this pipe section. Add elevation change, fittings losses, and required delivery pressure to get total system head.
Frequently Asked Questions
Does this include minor losses from bends and fittings?
No - this calculator covers major friction losses in straight pipe only. For fittings, valves, and bends, add minor losses: h_minor = K × V²/(2g), where K is the loss coefficient for each fitting. Total head loss = major losses + all minor losses.
How does pipe diameter affect head loss?
Head loss is very sensitive to pipe diameter. The Darcy-Weisbach equation shows h_f ∝ 1/D × V². Since Q = V × A = V × πD²/4, substituting gives h_f ∝ 1/D⁵. Doubling pipe diameter reduces head loss by a factor of 32 - a huge difference. This is why pipe sizing is so critical in hydraulic system design.
What is the "velocity head" shown in results?
Velocity head = V²/(2g) in meters. It represents the kinetic energy of the flow. The Darcy-Weisbach equation multiplies it by f×(L/D) to get friction head loss. It's also the pressure recovery you get when flow comes to a sudden stop (Bernoulli's theorem).
Related Tools
📊 Moody Chart Calculator
Get the friction factor (f) you need for this head loss calculation.
📉 Pressure Drop Calculator
Same calculation but results in Pascals (Pa) instead of meters.
⚙️ Pump Power Calculator
Use head loss from this tool to size your pump motor power.
🌊 Reynolds Number Calculator
Find Re before looking up friction factor on the Moody Chart.
⚡ Velocity Calculator
Find flow velocity from flow rate and pipe diameter.