Inputs
Results are estimates. Velocity limits are general rules of thumb; bends and fitting losses are not included. Also check working pressure, burst pressure and end fittings when choosing a hose.
Print / PDF
When you print, usage data (calculated values and the information you entered) is sent to Sistemay; your e-mail is not used for contact unless you give consent. Choose “Save as PDF” in the print dialog.Formulas and method
The inside diameter comes from the flow area, which is flow divided by the target velocity; the result is rounded up to the next standard SAE dash size.
Target velocities by line: suction 0.6–1.2 m/s, return 1.5–4 m/s, pressure roughly 4–6 m/s depending on pressure.
A [mm²] = Q [L/min] × 16.667 ÷ v [m/s]
d [mm] = √(4 × A ÷ π)
Re = v × d ÷ ν ; λ = 64/Re (laminar), 0.3164/Re^0.25 (turbulent)
Δp [bar] = λ × (L ÷ d) × ρ × v² ÷ 2 ÷ 10⁵ (ρ = 870 kg/m³)
Worked example
Example: 40 L/min, 160 bar pressure line (target 5 m/s) → required ID ≈ 13 mm → choose -10 (5/8"); actual speed ≈ 3.4 m/s, loss ≈ 0.5 bar over 3 m with ISO VG 46 oil.
Practical tips
- Keep the suction line short and large; high suction velocity causes pump cavitation.
- High velocity in the return line causes foaming and back pressure.
- A smaller hose means heat and energy loss; viscosity falls with hot oil and loss rises with cold oil.
- Choose hose type (1SN, 2SN, 4SP etc.) and fittings by working pressure for the selected size.
Frequently asked questions
How do I choose hydraulic hose size?
Divide flow by the target velocity for the line type to get the area, then round the diameter up to the next standard size.
Why must suction velocity be low?
High velocity lowers pressure at the pump inlet and causes cavitation, so keep it below 1.2 m/s.
What is an SAE dash size?
The dash number is the hose inside diameter in sixteenths of an inch; -8 is about 1/2", -10 about 5/8".
Why does pressure drop matter?
Line loss turns energy into heat and lowers efficiency; long lines may need a larger size.
Related products and tools
Looking for hoses and fittings?
Share the size you chose and we will quote the right hydraulic hoses and fittings.