Hydraulic Hose Sizes: Complete Sizing Chart & Selection Guide
Hydraulic hose size is expressed as a dash numberrepresenting the inside diameter (ID) in sixteenths of an inch. A -8 hosehas an ID of 8/16 inch = 1/2 inch. A -12 hose= 3/4 inch ID. Size and pressure rating are selected based on flow rate, operating pressure, and fluid velocity requirements.
Understanding Hydraulic Hose Dash Sizes
Every hydraulic hose has a dash size designation — a negative number that appears on the hose lay line and in product specifications. The dash number is the single most important sizing reference in hydraulic hose work, and understanding it eliminates the most common ordering and compatibility errors.
This convention is standardized across SAE J517 and used by all major hose manufacturers and is the standard used across the industry.
Fittings use the same convention: a -8 hose uses -8 end fittings. The dash sizes are matched across the assembly.
The dash number refers specifically to the inside diameter (ID)— the bore through which fluid flows. Outside diameter (OD) varies considerably between hose types, constructions, and manufacturers even at the same dash size, because reinforcement layers and cover thickness differ. Never use OD to identify or specify hydraulic hose size.
Complete Hydraulic Hose Size Chart
The following table covers the full range of standard hydraulic hose dash sizes from -3 through -48, with inside diameter in both fractional inches and millimeters.
| Dash Size | ID (inches) | ID (fraction) | ID (mm) | Typical Application |
|---|---|---|---|---|
| -3 | 0.188 in | 3/16 in | 4.8 mm | Pilot lines, instrument lines |
| -4 | 0.250 in | 1/4 in | 6.4 mm | Pilot lines, case drain, small flow |
| -5 | 0.313 in | 5/16 in | 7.9 mm | Small flow hydraulic circuits |
| -6 | 0.375 in | 3/8 in | 9.5 mm | General hydraulic service, low-to-medium flow |
| -8 | 0.500 in | 1/2 in | 12.7 mm | Most common — general mobile & industrial hydraulics |
| -10 | 0.625 in | 5/8 in | 15.9 mm | Medium flow hydraulic circuits |
| -12 | 0.750 in | 3/4 in | 19.1 mm | High-flow mobile hydraulics, steering circuits |
| -16 | 1.000 in | 1 in | 25.4 mm | High-flow circuits, loader and excavator applications |
| -20 | 1.250 in | 1-1/4 in | 31.8 mm | Large flow hydraulic systems |
| -24 | 1.500 in | 1-1/2 in | 38.1 mm | Large mobile equipment, industrial systems |
| -32 | 2.000 in | 2 in | 50.8 mm | High-volume industrial hydraulics |
| -40 | 2.500 in | 2-1/2 in | 63.5 mm | Very large flow systems |
| -48 | 3.000 in | 3 in | 76.2 mm | Large industrial / offshore hydraulics |
Inside diameters are nominal values per SAE J517. Actual measured IDs may vary slightly by manufacturer and hose construction. Source: SAE International — SAE J517.
Working Pressure by Size — SAE 100R2 Reference
Working pressure ratings vary by hose size within the same hose type. Smaller diameter hose of the same construction carries a higher pressure rating because the ratio of wall thickness to bore is more favorable. The following table shows working pressure ratings for SAE 100R2AT — the most common two-wire braid hydraulic hose used in mobile equipment applications.
| Dash Size | ID | WP (PSI) | WP (bar) | Min. Burst (PSI) |
|---|---|---|---|---|
| -4 | 1/4 in | 5,800 PSI | 400 bar | 23,200 PSI |
| -6 | 3/8 in | 4,000 PSI | 275 bar | 16,000 PSI |
| -8 | 1/2 in | 3,500 PSI | 240 bar | 14,000 PSI |
| -10 | 5/8 in | 3,000 PSI | 210 bar | 12,000 PSI |
| -12 | 3/4 in | 2,750 PSI | 190 bar | 11,000 PSI |
| -16 | 1 in | 2,250 PSI | 155 bar | 9,000 PSI |
| -20 | 1-1/4 in | 1,625 PSI | 112 bar | 6,500 PSI |
| -24 | 1-1/2 in | 1,500 PSI | 103 bar | 6,000 PSI |
| -32 | 2 in | 1,250 PSI | 86 bar | 5,000 PSI |
SAE 100R2AT working pressures. Ratings vary by manufacturer — always verify the specific product data sheet. For full pressure conversion reference, see our PSI to Bar Conversion Guide.
Fluid Velocity & Why It Drives Size Selection
The most technically correct method for selecting hydraulic hose size is based on fluid velocity— the speed at which fluid travels through the hose. Excessive velocity causes turbulence, heat generation, pressure drop, erosion, and system inefficiency. Too low a velocity in suction lines can cause cavitation at the pump.
Velocity formula: V (ft/sec) = Flow (GPM) × 0.3208 ÷ Area (in²)
Simplified: Required ID (in) = √(Flow (GPM) ÷ (2.448 × max velocity (ft/sec)))
Quick Flow Rate Reference by Dash Size
| Dash Size | ID | Max Flow at 25 ft/sec (pressure line) | Max Flow at 10 ft/sec (return line) |
|---|---|---|---|
| -4 | 1/4 in | ~3 GPM | ~1.2 GPM |
| -6 | 3/8 in | ~7 GPM | ~2.8 GPM |
| -8 | 1/2 in | ~12 GPM | ~4.9 GPM |
| -10 | 5/8 in | ~19 GPM | ~7.6 GPM |
| -12 | 3/4 in | ~27 GPM | ~10.9 GPM |
| -16 | 1 in | ~49 GPM | ~19.4 GPM |
| -20 | 1-1/4 in | ~76 GPM | ~30.4 GPM |
| -24 | 1-1/2 in | ~110 GPM | ~44 GPM |
Approximate maximum flow rates based on recommended fluid velocities. Actual system design should account for total pressure drop, fluid viscosity, and line length.
Step-by-Step Hose Size Selection
Common Sizing Mistakes to Avoid
Undersizing the Hose
Using a hose that is too small for the flow rate creates excessive fluid velocity, generating heat, increasing back pressure, and accelerating hose wear. Systems with undersized hose run hot, operate inefficiently, and experience premature component failure.
Oversizing the Return Line
Return lines are sometimes oversized unnecessarily, increasing cost and routing difficulty. While return lines need larger ID than pressure lines for the same flow rate, significantly oversizing them reduces fluid velocity below optimal and can lead to poor fluid conditioning performance.
Measuring OD Instead of ID
Measuring the outside diameter to determine hose size is one of the most common field errors. Two hoses of the same dash size from different manufacturers can have significantly different outside diameters due to different reinforcement and cover construction. Always measure ID or reference the lay line dash size.
Assuming Same Dash Size = Same Pressure Rating
A -8 SAE 100R1 hose has a different working pressure rating than a -8 SAE 100R2 hose of the same ID. Always verify the pressure rating for the specific hose type, not just the dash size. For full pressure rating context, see our guide: Hydraulic System Pressure Testing.
Frequently Asked Questions
The dash number represents the inside diameter in sixteenths of an inch. A -8 hosehas an ID of 8/16 inch = 1/2 inch. A -12 hosehas an ID of 12/16 inch = 3/4 inch. This convention is standardized across SAE J517 and used by all major manufacturers.
Measure the inside diameter (ID)using calipers on a cut cross-section, or read the dash size from the lay line printed on the hose. Do not measure the outside diameter — OD varies significantly between hose types even at the same dash size and will give an incorrect result.
No — it is the opposite. For the same hose type and construction, larger ID hoses have lower working pressure ratingsthan smaller ID hoses. A -4 hose of SAE 100R2 construction carries 5,800 PSI WP, while a -16 of the same type carries only 2,250 PSI WP. Always verify the specific pressure rating for the exact hose size and type.
The most common sizes in general mobile and industrial hydraulic work are -6 (3/8 in), -8 (1/2 in), -10 (5/8 in), -12 (3/4 in), and -16 (1 in). Team ARG stocks all of these in standard hose types for same-day availability at branch locations.
Select size based on flow rate (GPM), line type (pressure, return, or suction), and target fluid velocity. Pressure lines: 15–25 ft/sec. Return lines: 5–10 ft/sec. Suction lines: 2–4 ft/sec. Then verify the selected size meets the working pressure requirement for the hose type you are using.
Yes — a -8 hose uses -8 end fittings. The dash sizing convention is consistent across hose and fittings in the SAE system. However, always verify compatibility between specific hose and fitting products from the same or different manufacturers rather than assuming all -8 products are interchangeable without review.
A -8 hydraulic hose has an inside diameter of 1/2 inch, which equals 12.7 mm. In metric hose systems, this is equivalent to DN12 (nominal diameter 12 mm) or a 1/2 inch bore designation.