Pressure drop calculator Hose flow, to the millibar.
Bore, length and flow in; pressure drop, velocity and flow regime out, with every step of the sum shown.
Calculate
Liquids · smooth bore · metric or imperial
Pressure drop
0.361bar
over 20 m of Ø 25 mm hose, 60 L/min of water at 20 °C.
= 36.1 kPa · 3.69 m of head
K 0.3 per bend, radius at least 3 × bore. Bend length: bend radius calculator
Outlet above the inlet. Negative if it runs downhill.
Velocity
Reynolds number
Friction factor
Where the pressure goes
Assumptions: a Newtonian liquid at the stated temperature, a smooth bore (ε 0.0015 mm), K 0.3 per 90° bend and an open outlet. A first estimate for sizing, not a guarantee of performance. Smooth-bore hoses
How it’s worked out
Darcy–Weisbach, with your numbers in it.
Pressure drop is the pressure a liquid loses on its way through a hose: friction against the wall along the whole length, an extra loss at every bend and the height it has to climb. It decides the pump you need and whether the flow arrives where it should.
The bore matters more than anything else. At the same flow, a hose one size smaller can lose three or four times as much pressure, which is why sizing the line is the first thing to settle, before the hose is ordered.
Δp = f · LD · ρv²2 + ΣK · ρv²2 + ρgΔz
- f
- Darcy friction factor
- L
- Hose length
- D
- Inside diameter (bore)
- ρ
- Density of the liquid
- v
- Mean velocity, Q ÷ bore area
- K
- Loss coefficient of a bend
- Δz
- Height of the outlet over the inlet
- Re
- Reynolds number, ρvD ÷ μ
Your case, line by line
Water · 20 °C (ρ 998.2 kg/m³, μ 1.002 mPa·s) through 20 m of Ø 25 mm hose, 2 bends. Worked in SI units.
- Flow Set by you 60 L/min
- Velocity v = Q ÷ (πD²/4) = 1 L/s ÷ 4.91 cm² 2.04 m/s
- Reynolds number Re = ρvD/μ = 998 × 2.04 × 0.025 ÷ 0.001002 50,700
- Friction factor Colebrook–White, ε/D = 0.00006 0.021
- Friction f · L/D · ρv²/2 = 0.021 × 800 × 2,070 Pa 0.349 bar
- Bends n · K · ρv²/2 = 2 × 0.3 × 2,070 Pa 0.0124 bar
- Height ρ · g · Δz = 998 × 9.81 × 0 m 0 bar
- Total pressure drop Friction + bends + height 0.361 bar
A · Across the bore
B · Along the hose
C · On the Moody chart
Questions
What engineers ask before they size a line.
01 How do you calculate pressure drop in a hose?
With the Darcy–Weisbach equation, Δp = f · (L/D) · ρv²/2. The friction factor f is 64/Re when the flow is laminar and comes from the Colebrook–White equation when it is turbulent. Each bend adds K · ρv²/2, and lifting the liquid adds ρgΔz.
02 How much does the bore change the pressure drop?
More than any other input. At the same flow in turbulent conditions, pressure drop falls with nearly the fifth power of the bore: a 19 mm hose loses about 3.7 times as much as a 25 mm one.
03 What velocity does CIP cleaning need?
At least 1.5 m/s in the line, the figure EHEDG hygienic-design guidance works to, because it keeps the flow turbulent right at the wall. The calculator flags whether your duty reaches it.
04 Laminar or turbulent: why does it matter?
Below a Reynolds number of about 2,300 the flow is laminar and pressure drop grows in step with flow. Above about 4,000 it is turbulent and grows almost with the square of the flow. In between, the flow switches from one to the other and losses are hard to predict.
05 Does it work for gases, steam or slurries?
No. It is written for liquids that behave like water: Newtonian and incompressible. Gases and steam change density along the hose, and slurries or thick products need their own model. Send us the duty and an engineer will size it.