Moody Chart Friction Factor Calculator
The Darcy friction factor f relates pressure drop to flow via the Darcy-Weisbach equation: hf = f × (L/D) × (V²/2g). f depends on Reynolds number (Re) and relative roughness (ε/D)....
Formula
Source: White, F.M. (2016) Fluid Mechanics 8th ed.; Moody (1944); Colebrook (1939); Swamee-Jain (1976) | Last reviewed: July 3, 2026
Examples
100000 reynolds
= 0.0205 friction_factor
- roughness = 0.045
- diameter = 100
- material = commercial_steel
Re=100,000, commercial steel (ε/D=0.00045) → f = 0.0205
1000 reynolds
= 0.064 friction_factor
- roughness = 0.045
- diameter = 100
Re=1,000 (laminar) → f = 64/1000 = 0.064
1000000 reynolds
= 0.0185 friction_factor
- roughness = 0.045
- diameter = 100
Re=1,000,000, commercial steel → f = 0.0185 (fully turbulent)
Quick Reference Table
| Material | ε (mm) | ε (ft) | ε/D for 100 mm pipe |
|---|---|---|---|
| Drawn tubing (glass, plastic) | 0.0015 | 0.000005 | 0.000015 |
| Commercial steel | 0.045 | 0.00015 | 0.00045 |
| Galvanized iron | 0.15 | 0.0005 | 0.0015 |
| Cast iron | 0.26 | 0.00085 | 0.0026 |
| Concrete | 0.3-3.0 | 0.001-0.01 | 0.003-0.03 |
| Riveted steel | 0.9-9.0 | 0.003-0.03 | 0.009-0.09 |
| Wood stave | 0.5 | 0.0017 | 0.005 |
Where is this used?
Used for: 1) Pressure drop in piping systems (water, oil, gas, steam), 2) Compressor and pump suction line sizing, 3) Heat exchanger pressure drop, 4) HVAC duct pressure drop, 5) Pipeline hydraulic design, 6) Pump performance verification.
The most common reference is the Moody chart (Moody, 1944), which plots f vs Re for various ε/D values.
Modern calculations use the Swamee-Jain explicit formula (1976) or solve the Colebrook-White equation iteratively.
Real-World Usage Scenarios
Process Water Main Pressure Drop
A 6-inch Schedule 40 commercial steel pipe (D = 154 mm) carries 500 GPM water at 25°C (ρ = 997 kg/m³, μ = 8.9e-4 Pa·s). V = 500 × 0.0000631 / (π × 0.077²) = 1.69 m/s. Re = 997 × 1.69 × 0.154 / 8.9e-4 = 292,000. ε/D = 0.045/154 = 0.00029. Swamee-Jain f = 0.25 / [log₁₀(0.00029/3.7 + 5.74/292000^0.9)]² = 0.25 / [log₁₀(7.84e-5 + 0.0001016)]² = 0.25 / [log₁₀(0.000180)]² = 0.25 / (-3.745)² = 0.25/14.02 = 0.0178. Pressure drop per 100 m: hf = 0.0178 × (100/0.154) × (1.69² / (2×9.81)) = 1.68 m.
Common Mistakes to Avoid
Confusing Darcy and Fanning friction factor
The Darcy friction factor (this calculator) is 4× the Fanning friction factor. Many older chemical engineering texts use Fanning. Verify which one your source uses. Converting: f_Darcy = 4 × f_Fanning. The pressure drop formula is hf = f × L/D × V²/2g, with f being the Darcy factor; the Fanning-based formula is hf = 4f × L/D × V²/2g.
Using 64/Re for turbulent flow
f = 64/Re only applies to LAMINAR flow (Re < 2,300). For turbulent flow, f is much smaller and depends on ε/D, not just Re. Using 64/Re for turbulent flow over-predicts friction loss by 2-5x.
Industry Standards Referenced
Frequently Asked Questions
What is the difference between Colebrook-White, Swamee-Jain, and Haaland?
Colebrook-White (1939) is the original implicit equation: 1/√f = -2.0 × log₁₀((ε/D)/3.7 + 2.51/(Re√f)). It must be solved iteratively. Swamee-Jain (1976) is an explicit approximation: f = 0.25 / [log₁₀((ε/D)/3.7 + 5.74/Re^0.9)]². Accurate to ±1% for Re > 4,000. Haaland (1983) is another explicit approximation: 1/√f = -1.8 × log₁₀((ε/D/3.7)^1.11 + 6.9/Re). Accurate to ±1.5% over a wider range. Swamee-Jain is the most widely used for spreadsheet/handheld calculations.
How do I find the relative roughness ε/D?
From the pipe material's absolute roughness ε (mm or ft) and the pipe inside diameter D. ε for common materials: drawn tubing 0.0015 mm, commercial steel 0.045 mm, galvanized iron 0.15 mm, cast iron 0.26 mm, riveted steel 0.9-9 mm, concrete 0.3-3 mm. For aged pipes, use the higher end of the range (corrosion and fouling increase ε over time).
What roughness (ε) should I use for aged steel?
New commercial steel: ε=0.045mm. After 10+ years: ε=0.15-0.5mm depending on corrosion. Use higher range for conservative pressure drop estimates.
Reviewed for accuracy
Cross-referenced against White's Fluid Mechanics and Moody chart · Last reviewed: July 3, 2026
All calculations are for reference only. Always verify with manufacturer data and a qualified engineer for critical applications. Learn about our editorial process.