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Hydraulic Hose Selection Calculator

Select the correct hydraulic hose dash size from flow rate, pressure, and velocity limits. Calculates pressure drop and fitting losses.

About this calculator

Hydraulic hose sizing starts with velocity, not pressure — running fluid too fast through an undersized hose wastes energy, generates heat, and accelerates wear, so this calculator applies different maximum velocity limits depending on which side of the pump the hose sits on: 4 ft/s for suction lines (which must avoid cavitation from excessive vacuum), 15 ft/s for return lines, and 20 ft/s for pressure lines, which can tolerate more velocity because they're not vacuum-limited. From the selected max velocity and required flow (V = 0.3208 × GPM / ID²), it back-calculates the minimum inner diameter, then rounds up to the nearest standard SAE dash size (from -4 up to -32) and recalculates actual velocity with that real hose. Reynolds number (7740 × GPM / (ID × viscosity in cSt)) determines whether flow is laminar or turbulent, which in turn sets the friction factor used in the Darcy-Weisbach-based pressure-drop calculation — laminar flow uses 64/Re directly, while turbulent flow uses an empirical 0.316/Re^0.25 approximation valid for smooth-bore hose.

Fitting losses are approximated as 2 ft of equivalent hose length per fitting. The tool also checks the selected hose's SAE 100R2AT pressure rating against your specified working pressure to flag over-pressurized selections, and converts total pressure drop into horsepower lost to friction. Because velocity limits and viscosity assumptions are generalized rules of thumb, always confirm the final selection against the hose manufacturer's actual pressure rating and the fluid's real operating viscosity, which changes significantly with temperature.

Inputs

psi
ft

Results

Recommended SAE dash size

8

Hose ID (inches)0.5
Minimum required ID (in)0.4
Actual velocity (ft/s)12.83
Total pressure drop (PSI)5.3
Reynolds number4,838
Pressure rating usage (%)75
Power loss (HP)0.03
Velocity LabelPressure (≤20 ft/s)
How to Use This Calculator
  1. Enter Flow rate (GPM), Working pressure (PSI), and Hose length (ft).
  2. Set Line type (1=suction, 2=return, 3=pressure), Fluid specific gravity, and Fluid viscosity (cSt).
  3. Adjust Number of fittings as needed.
  4. Review the Recommended SAE dash size result.
  5. Use Hose ID (inches) and Minimum required ID (in) to inform your decision.

What each input means

Flow rate (GPM)
Hydraulic flow rate in gallons per minute.
Working pressure (PSI)
Maximum system working pressure.
Hose length (ft)
Total hose run length in feet.
Line type (1=suction, 2=return, 3=pressure)
Suction lines need larger ID (low velocity); pressure lines allow higher velocity.
Fluid specific gravity
Hydraulic fluid specific gravity (0.87 typical for petroleum oil).
Fluid viscosity (cSt)
Kinematic viscosity at operating temperature (32 cSt typical for ISO VG 32).
Number of fittings
Number of hose end fittings and adapters in the run.

What each result means

Recommended SAE dash size
SAE dash size (-4, -6, -8, etc.) for the hose assembly.
Hose ID (inches)
Inner diameter of the selected hose.
Minimum required ID (in)
Calculated minimum ID to stay within velocity limits.
Actual velocity (ft/s)
Fluid velocity with the selected hose size.
Total pressure drop (PSI)
Pressure loss through hose and fittings.
Reynolds number
Flow regime indicator (<2300 = laminar, >4000 = turbulent).
Pressure rating usage (%)
Working pressure as percentage of SAE 100R2AT hose rating.
Power loss (HP)
Hydraulic power lost to friction in the hose run.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Flow rate (GPM) = 10, Working pressure (PSI) = 3000, Hose length (ft) = 10, Line type (1=suction, 2=return, 3=pressure) = 3 = 7 input(s) provided
  2. Calculate Recommended SAE dash size
    Recommended SAE dash size
    8 = 8
  3. Calculate Hose ID
    Hose ID
    0.5 = 0.5
  4. Calculate Minimum required ID
    Minimum required ID = sqrt(0.3208 * flowGpm / maxVelocity)
    0.4 = 0.4

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.

Frequently Asked Questions

Why does Line Type change the recommended hose size so much for the same flow rate?

Each line type carries a different maximum allowable velocity — 4 ft/s for suction, 15 ft/s for return, and 20 ft/s for pressure lines — and the calculator solves for minimum ID as sqrt(0.3208 × GPM / max velocity), so a lower velocity limit forces a larger required diameter for the same flow. Suction lines need the most generous sizing because excessive vacuum there risks pump cavitation, a failure mode return and pressure lines don't share.

What does the Reynolds Number tell me, and how is it used to pick a pressure-drop formula?

Reynolds number (7740 × GPM ÷ (ID × viscosity in cSt)) indicates whether flow is smooth (laminar, below 2300) or chaotic (turbulent, above roughly 4000), and the calculator picks a different friction factor for each: 64/Re for laminar flow, or an empirical 0.316/Re^0.25 approximation for turbulent flow. Since friction factor feeds directly into the pressure-drop calculation, which regime you're in changes how pressure loss scales with velocity.

Why might Pressure Rating Usage show over 100%?

The calculator looks up the SAE 100R2AT working-pressure rating for the selected dash size and divides your entered Working Pressure by it — if your working pressure exceeds that hose's rating, the percentage exceeds 100, flagging that the selected hose size is under-rated for the application even though it may satisfy the velocity requirement. In that case, a higher-rated hose construction or a larger dash size with more pressure headroom is needed.

How does the Number of Fittings input affect the results if fittings aren't hose length?

Each fitting is converted into 2 feet of equivalent straight hose length and added into the same Darcy-Weisbach pressure-drop calculation used for the straight run, so more fittings directly increase Total Pressure Drop and Power Loss without changing the physical hose length or the recommended dash size. This equivalent-length approach is a simplification — actual losses vary by fitting geometry (elbows, tees, quick-connects all differ).

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