Pressure Drop Calculator
Calculate pressure loss through AN hose lines using the Darcy-Weisbach equation with Swamee-Jain friction factor. Accounts for pipe length, fluid properties, fittings and minor losses. Compare all AN dash sizes side-by-side.
Fluid
AN Dash Size
Fittings / Minor Losses
90Ā° Elbow (standard)
Le/D = 30
45Ā° Elbow
Le/D = 16
Tee (straight through)
Le/D = 20
Tee (branch)
Le/D = 60
Gate valve (fully open)
Le/D = 8
Ball valve (fully open)
Le/D = 3
In-line filter
Le/D = 150
Fittings add ~0.57 m equivalent length ā effective length 2.57 m
Pressure Drop ā AN-6 Ā· 9.5mm Ā· Petrol / Gasoline Ā· 300 L/h Ā· 2.0 m
Pressure Drop
0.564
PSI
Pressure Drop
3.89
kPa
Pressure Drop
0.0389
bar
Flow Velocity
1.18
m/s
Pressure Drop Comparison @ 300 L/h Ā· 2.0 m Ā· Petrol / Gasoline
| Dash | ID (mm) | Velocity (m/s) | ĪP (PSI) | ĪP (kPa) | Reynolds | Rating |
|---|---|---|---|---|---|---|
| AN-3 | 4.8 | 4.61 | 11.548 | 79.62 | 29,741 | Critical |
| AN-4 | 6.4 | 2.59 | 2.895 | 19.96 | 22,306 | Good |
| AN-6 | 9.5 | 1.18 | 0.439 | 3.03 | 15,027 | Excellent |
| AN-8 | 12.7 | 0.66 | 0.111 | 0.76 | 11,241 | Excellent |
| AN-10 | 15.9 | 0.42 | 0.038 | 0.26 | 8,978 | Excellent |
| AN-12 | 19.1 | 0.29 | 0.016 | 0.11 | 7,474 | Excellent |
| AN-16 | 25.4 | 0.16 | 0.004 | 0.03 | 5,620 | Excellent |
| AN-20 | 31.8 | 0.10 | 0.001 | 0.01 | 4,489 | Excellent |
Methodology
Darcy-Weisbach: ĪP = fĀ·(L/D)Ā·(ĻvĀ²/2). Friction factor f uses Hagen-Poiseuille (Re < 2 300) for laminar flow, and Swamee-Jain for turbulent flow ā an explicit approximation of the Colebrook equation accurate to Ā±3%.
Equivalent Length Method: Fittings are modelled as equivalent pipe lengths (Le/D). A 90Ā° elbow adds the equivalent pressure drop of 30 pipe diameters of straight pipe. This is the standard industrial method.
Pipe Roughness: AN PTFE hose roughness assumed at 0.0015 mm (smooth bore). Stainless braided rubber is slightly rougher (~0.003 mm) but the effect is minimal at typical motorsport Reynolds numbers.
Severity Guide: For fuel systems, keep pressure drop below 1 PSI per meter of line. For oil return lines, below 2 PSI total. High pressure drops starve the engine ā size up one AN dash if >3 PSI is shown.