Choosing the wrong hose size causes heat buildup, pressure drop, and premature hose failure. Use this guide to select the correct dash size, verify flow velocity, and match your hose to the right pressure rating.
The dash size system is a standardized shorthand for hose inside diameter, used universally across the North American hydraulic industry.
Each dash number represents the hose inside diameter in sixteenths of an inch. So a -8 hose has an inside diameter of 8/16" = 1/2". A -12 hose = 12/16" = 3/4".
This system applies to both the hose ID and to the fittings installed on that hose. A -8 hose will use -8 fittings. Knowing your dash size eliminates most of the guesswork when ordering replacement hose assemblies.
Dash sizes are also used for metric hose using an equivalent convention, but note that metric hose outside diameters differ from the North American standard, so always verify when ordering internationally sourced equipment.
| Dash Size | ID (inches) | ID (mm) | Common Use | Typical Flow Range | Pressure Notes |
|---|---|---|---|---|---|
| -4 | 1/4" | 6.35 mm | Instrumentation / pilot lines | 1–3 GPM | High (3,000–5,000 PSI typical) |
| -6 | 3/8" | 9.5 mm | Return lines / low pressure | 3–8 GPM | Medium (2,500–4,000 PSI typical) |
| -8 | 1/2" | 12.7 mm | General hydraulics | 5–15 GPM | Medium-High (2,000–3,500 PSI typical) |
| -10 | 5/8" | 15.9 mm | Medium pressure systems | 10–25 GPM | Medium (1,750–3,000 PSI typical) |
| -12 | 3/4" | 19.0 mm | High flow systems | 20–40 GPM | Medium (1,500–2,750 PSI typical) |
| -16 | 1" | 25.4 mm | Large equipment | 35–70 GPM | Medium (1,250–2,500 PSI typical) |
| -20 | 1-1/4" | 31.8 mm | Heavy equipment | 60–120 GPM | Lower (1,000–2,000 PSI typical) |
| -24 | 1-1/2" | 38.1 mm | Industrial systems | 90–180 GPM | Lower (750–1,750 PSI typical) |
| -32 | 2" | 50.8 mm | High volume return lines | 150–300 GPM | Low (500–1,500 PSI typical) |
Flow ranges are guidelines for petroleum-based hydraulic fluid at standard viscosity (ISO VG 46). Actual capacity depends on system pressure, fluid viscosity, hose length, and fittings. Always verify with system-specific calculations.
Not all hydraulic hose is the same. Construction type determines pressure rating, flexibility, and temperature range.
| Hose Type | Construction | Available Sizes | Max Pressure Range | Temp Range | Best For |
|---|---|---|---|---|---|
| SAE 100R1 | Single wire braid | -4 to -32 | 5,800 PSI (–4) to 250 PSI (–32) | -40°F to +212°F | Medium pressure general hydraulics |
| SAE 100R2 | Double wire braid | -4 to -32 | 7,250 PSI (–4) to 400 PSI (–32) | -40°F to +212°F | High pressure hydraulics |
| SAE 100R15 | Spiral wound (4-6 wire) | -8 to -32 | 6,000 PSI (–8) to 2,000 PSI (–32) | -40°F to +250°F | Very high pressure, pulsing systems |
| Thermoplastic (SAE 100R7/R8) | Polyester braid over thermoplastic core | -4 to -16 | 5,000 PSI (–4) to 1,500 PSI (–16) | -70°F to +200°F | Clean environments, washdown applications |
Follow these steps to select the correct hose for any hydraulic application.
Start with the pump output in gallons per minute. For mobile equipment, check the machine specifications. For industrial systems, calculate from pump displacement (cc/rev) × RPM ÷ 231 = GPM. If you have a flow meter, use measured data, pump specs are theoretical maximums.
Velocity (ft/s) = (0.3208 × GPM) ÷ ID² (in inches squared). This formula gives you the fluid velocity in feet per second. Compare against the recommended velocity ranges for your line type. Exceeding these limits causes heat, erosion, and premature hose failure.
Use the velocity calculation to confirm your dash size selection from the chart. If your calculated velocity is above the recommended range, move up one dash size. If it's in range, you have the correct size. Always round up when between sizes, undersized hose is the more costly mistake.
Check the hose working pressure rating against your system's maximum operating pressure. The hose working pressure must exceed the system's peak pressure, not just average pressure. Include a 4:1 safety factor minimum (hose burst pressure should be 4× working pressure), which is built into SAE-rated hose.
Fluid velocity is the most important factor in hose sizing. Too fast causes turbulence, heat, and erosion. Too slow wastes material. These are the industry-standard target velocity ranges:
Pressure Lines
10–15 ft/s
Main supply lines from pump to actuator
Return Lines
5–10 ft/s
Low-pressure return to tank
Suction Lines
2–4 ft/s
Inlet to pump, critical for cavitation prevention
These errors are responsible for most premature hose failures in the field.
Always size hydraulic hose by inside diameter (ID), not outside diameter (OD). The OD varies depending on construction type (single braid, double braid, spiral). Two hoses with the same ID can have very different ODs. Using OD to determine dash size will lead to the wrong fitting selection.
Suction lines (pump inlet) require larger hose than you might expect. Undersized suction lines cause cavitation, gas bubble formation in the pump, which destroys pump internals within hours. Always size suction lines to keep velocity below 4 ft/s and use suction-rated hose with wire helix reinforcement to prevent collapse.
Hose catalogs list working pressure, not burst pressure. SAE-rated hose has a minimum 4:1 safety factor (burst is 4× working pressure). When comparing hoses, always compare working pressure ratings, never try to calculate burst pressure as your operating limit.
Our specialists stock every common hose size and can cut and crimp assemblies same-day at our Cleveland, TN location. Call us or bring in your old hose for a direct match.
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