Pressure Drop Calculator

Free online pressure drop calculator for pipes and ducts. Calculate pressure loss for water, air, and gas flow using Darcy-Weisbach equation. Essential for HVAC, plumbing, and fluid mechanics.

The Pressure Drop Calculator helps you calculate pressure loss due to friction in pipes and ducts. Enter pipe dimensions, flow rate, and fluid properties to determine pressure drop, head loss, and flow velocity using the Darcy-Weisbach equation.

What is Pressure Drop?

Pressure drop (also called pressure loss or head loss) is the reduction in fluid pressure as it flows through a pipe due to friction between the fluid and pipe wall. This phenomenon occurs in all fluid systems and must be calculated to ensure adequate flow rates, proper pump sizing, and efficient system design. Pressure drop depends on pipe diameter, length, roughness, fluid properties (density, viscosity), and flow velocity. The Darcy-Weisbach equation is the most accurate method for calculating pressure drop in pipes.

How to Use the Pressure Drop Calculator

Select the fluid type (water, air, steam, oil, or natural gas)
Enter pipe diameter and length in your preferred units
Select pipe material or enter custom roughness coefficient
Enter either flow rate (volume per time) or flow velocity
Optionally adjust temperature if different from standard conditions
Click Calculate to see pressure drop, head loss, and flow characteristics
Results include Reynolds number and friction factor for analysis

Pressure Drop Formulas

1. Darcy-Weisbach: ΔP = f × (L/D) × (ρv²/2)

2. Head Loss: h = ΔP / (ρ × g)

3. Reynolds Number: Re = (ρ × v × D) / μ

Where: ΔP = pressure drop, f = friction factor, L = length, D = diameter, ρ = density, v = velocity, μ = viscosity, g = gravity

Flow Regimes

Laminar Flow (Re < 2,300): Smooth, predictable flow in layers

Transition (2,300 < Re < 4,000): Unstable, unpredictable flow

Turbulent Flow (Re >4,000): Chaotic mixing, most common in practice

Factors Affecting Pressure Drop

Pipe Diameter: Smaller diameter = higher pressure drop (inverse 4th power relationship)

Pipe Length: Longer pipes = more pressure drop (linear relationship)

Flow Velocity: Higher velocity = much higher pressure drop (squared relationship)

Surface Roughness: Rougher pipes = higher friction = more pressure drop

Fluid Viscosity: Higher viscosity = more resistance = more pressure drop

Applications

HVAC: Duct design, air flow calculations, fan selection
Plumbing: Water supply systems, pipe sizing, pump selection
Fire protection: Sprinkler systems, hydrant flow calculations
Chemical plants: Process piping, flow assurance
Oil & Gas: Pipeline design, flow rate optimization
Industrial: Compressed air systems, hydraulic systems
Building systems: Hot/cold water distribution, drainage

Tips for Minimizing Pressure Drop

Use larger diameter pipes when possible - doubling diameter reduces pressure drop by 94%
Minimize pipe length and number of fittings/bends
Keep pipes clean and smooth - roughness significantly increases friction
Avoid sudden changes in diameter - use gradual transitions
Consider flow velocity - keep below 2 m/s for water to minimize noise and erosion
Account for fittings and valves - they add equivalent pipe length
Select appropriate pipe material for the fluid and application

Design Guidelines

Typical design velocities: Water pipes 1-3 m/s (residential), 1.5-4.5 m/s (commercial); Air ducts 3-8 m/s (supply), 2-5 m/s (return). Maximum recommended pressure drop per 100m: Water pipes 400-800 Pa (residential), 500-1000 Pa (commercial); Air ducts 0.8-1.5 Pa/m (low velocity), 1.5-4 Pa/m (high velocity). Always verify that available pump/fan pressure exceeds total system pressure drop including fittings, valves, and equipment.

Pressure Drop Calculator

Fluid Type

Pipe Parameters

Flow Parameters