Friction Factor Calculator

What Is Darcy Friction Factor?

The Darcy friction factor is a dimensionless coefficient that quantifies how much energy or pressure is lost due to wall friction as a fluid moves through pipe or annular flow. It is the friction term used in the Darcy–Weisbach equation to calculate pressure loss per unit length for incompressible flow in pipes.

In drilling hydraulics, friction factor is central to estimating pressure losses in drill pipe, casing, surface lines, and the annulus. Those friction losses add directly to standpipe pressure and equivalent circulating density (ECD), so an accurate friction factor is important for staying inside the safe pressure window between pore pressure and fracture pressure.

The Darcy friction factor used here is four times the Fanning friction factor sometimes quoted in process design texts. When you compare values or charts, always check whether they are using Darcy or Fanning definitions so you don't mix them by mistake.

Friction Factor & Pressure Loss Formulas

For turbulent flow in rough pipes, this calculator uses the Moody explicit approximation to the Colebrook–White equation:

When pipe length and flow velocity are provided, the calculator also estimates pressure loss using the Darcy–Weisbach equation:

Where:

• f = Darcy friction factor (dimensionless)
• k = absolute roughness of the pipe or annulus wall (m, mm, in, ft)
• D = hydraulic diameter of the flow path (m, mm, in, ft)
• Re = Reynolds number (dimensionless)
• L = pipe length used for the pressure-loss estimate
• V = average flow velocity in the pipe or annulus
• ρ = fluid density in consistent units with the selected pressure units

Example Friction Factor and Pressure Drop Calculation

Consider water flowing in a steel line with hydraulic diameter D = 0.10 m, absolute roughness k = 0.000045 m (0.045 mm), Reynolds number Re = 100,000, pipe length L = 100 m, fluid density ρ ≈ 1,000 kg/m³, and average velocity V = 2 m/s.

This example shows how even a relatively small friction factor can generate noticeable pressure loss over long flow paths or at high velocities. In drilling hydraulics, longer intervals, smaller annular clearances, and higher flow rates all increase the friction term and therefore standpipe pressure and ECD.

Why Friction Factor Matters in Drilling Hydraulics

• Hydraulics design: Friction factor is a key input when sizing pumps, surface lines, and bit nozzles to achieve the desired flow rate and jet impact without exceeding equipment limits.
• ECD management: Higher friction factor increases annular pressure losses and therefore equivalent circulating density at bottomhole. This can reduce pressure margin to fracture and increase lost circulation risk.
• Well control margins: Accurate friction estimates help compare dynamic circulating pressures to MAASP and casing shoe limits during kill operations and high-rate circulation.
• Optimization: Adjusting flow rate, mud properties, and string design to manage friction factor can improve cuttings transport and hole cleaning while keeping standpipe pressure at a safe, efficient level.