Pipe Pressure Drop Calculator
Calculate how much pressure a fluid loses as it flows through a pipe - using the industry-standard Darcy-Weisbach equation. You'll need the friction factor from the Moody Chart Calculator first, then enter it here along with your pipe and fluid data.
Calculate Pressure Drop (Darcy-Weisbach)
Results
What Is Pipe Pressure Drop?
When fluid flows through a pipe, it loses energy due to friction between the fluid and the pipe wall, and between layers of fluid moving at different speeds. This energy loss shows up as a drop in pressure from one end of the pipe to the other.
Pressure drop matters because your pump has to overcome it. If your pump doesn't provide enough pressure to push fluid against friction losses, your system won't deliver the required flow rate. Getting this calculation right is essential for sizing pumps, selecting pipe diameters, and ensuring system efficiency.
The Darcy-Weisbach Formula Explained
ΔP = f × (L/D) × (ρV²/2) - ΔP - pressure drop (Pa = N/m²)
- f - Darcy friction factor (dimensionless, from the Moody Chart)
- L - pipe length (m)
- D - pipe internal diameter (m)
- ρ - fluid density (kg/m³)
- V - average flow velocity (m/s)
Head loss in meters is h_f = ΔP / (ρ × g), where g = 9.81 m/s². Head loss is useful when working with pump curves and hydraulic grade lines.
Where Does the Friction Factor Come From?
The friction factor f depends on the Reynolds number and pipe roughness. For laminar flow (Re < 2300), it's simply f = 64/Re. For turbulent flow, use the Moody Chart Calculator - it solves the Colebrook-White equation iteratively and gives you f to 4 significant figures.
Worked Example
Water (ρ = 1000 kg/m³) flows at 1.5 m/s through a 100 mm diameter, 50 m long commercial steel pipe. The friction factor from the Moody Chart is f = 0.019.
ΔP = 0.019 × (50 / 0.1) × (1000 × 1.5² / 2)
ΔP = 0.019 × 500 × 1125
ΔP = 10,688 Pa ≈ 10.7 kPa
Head loss: h_f = 10,688 / (1000 × 9.81) ≈ 1.09 m
Frequently Asked Questions
Does this calculator account for minor losses (bends, valves, fittings)?
No - this calculator covers major losses only (friction in straight pipe sections). For elbows, valves, tees, and other fittings, you need to add minor losses separately, typically using K-values or equivalent lengths.
How do I convert pressure drop to bar or psi?
1 bar = 100,000 Pa. 1 psi = 6,894.76 Pa. So divide your Pa result by 100,000 for bar, or by 6,895 for psi.
What happens to pressure drop if I double the pipe length?
Pressure drop is directly proportional to pipe length (L appears linearly in the equation). Double the length → double the pressure drop.
Related Tools
📊 Moody Chart Calculator
Get the friction factor (f) needed as input to this calculator.
💧 Head Loss Calculator
Calculate head loss in meters - useful for pump selection and pipe sizing.
🌊 Reynolds Number Calculator
Determine flow regime before looking up friction factor on the Moody Chart.
⚡ Velocity Calculator
Find flow velocity from flow rate and diameter - required input for this tool.
⚙️ Pump Power Calculator
Use head loss from this calculator to size your pump motor.