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Calculate your own Reynolds Number (engineeringtoolbox.com)

ISO 4406:1999 Code Chart
Range Code Particles Per Mililiter Particles Size
More Than Up To/Including
24 80,000 160,000 4μm[c]
23 40,000 80,000
22 20,000 40,000 6μm[c]
21 10,000 20,000
20 5,000 10,000
19 2,500 5,000 14μm[c]
18 1,300 2,500
17 640 1,300
16 320 640 Particles Size
15 160 320
14 80 160
13 40 80 4μm[c]
12 20 40
11 10 20
10 5 10 6μm[c]
9 2.5 5
8 1.3 2.5
7 0.64 1.3
6 0.32 0.64 14μm[c]
ISO Code Number Number of Particles Per ml
More Than Up To and Including
22 20,000 40,000
21 10,000 20,000
20 5,000 10,000
19 2,500 5,000
18 1,300 2,500
17 640 1,300
16 320 640
15 160 320
14 80 160
13 40 80
12 20 40
11 10 20
10 5 10
9 2.50 5
8 1.30 1.5
7 0.64 1.30

Recommended ISO Cleanliness Targets

ISO code numbers Type of system Typical components Sensitivity
23 / 21 / 17 Low pressure systems with large clearances Ram pumps Low
20 / 18 / 15

Typical cleanliness of new hydraulic oil straight from the manufacturer.

Low pressure heavy industrial systems or applications where long-life is not critical

 Low control valves cylinders Average
19 / 17 / 14 General machinery and mobile systems Medium pressure, medium capacity Gear pumps/motors Important
18 / 16 / 13

World Wide Fuel Charter cleanliness standard for diesel fuel delivered from the filling station nozzle.

High quality reliable systems

General machine requirements

 Injector valve and high pressure pumps/ motors Directional and pressure control valves Critical
17 / 15 / 12 Highly sophisticated systems and hydrostatic transmissions Proportional valves Critical
16 / 14 / 11

Performance servo and high Pressure long-life systems

e.g. Aircraft machine tools, etc.

 Industrial servovalves Critical
15 / 13 / 09

Silt sensitive control system with very high reliability

Laboratory or aerospace

 High performance servovalves Super Critical
Pumps <2000 psi
Fixed Gear 20/18/15
Fixed Piston 19/17/14
Fixed Vane 20/18/15
Variable Piston 18/16/13
Variable Vane 18/16/13
Valves <2000 psi
Cartridge 18/16/13
Check Valve 20/18/15
Directional (solenoid) 20/18/15
Flow Control 19/17/14
Pressure Control (modulating) 19/17/14
Proportional Cartridge Valve 17/15/12
Proportional Directional 17/15/12
Proportional Flow Control 17/15/12
Proportional Pressure Control 17/15/12
Servo Valve 16/14/11
Bearings <2000 psi
Ball Bearing 15/13/10
Gearbox (industrial) 17/16/13
Journal Bearing (high speed) 17/15/12
Journal Bearing (low speed) 17/15/12
Roller Bearing 16/14/11
Actuators <2000 psi
Cylinders 17/15/12
Vane Motors 20/18/15
Axial Piston Motors 19/17/14
Gear Motors 20/18/14
Radial Piston Motors 20/18/15
Test Stands, Hydrostatic <2000 psi
Test Stands 15/13/10
Hydrostatic Transmissions 17/15/13

ISO NAS SAE Cleanliness Conversion Table

ISO/DIS 4406 Defence Std. 05/42 NAS 1638 SAE 749
Table A Table B
13/11/08 2
14/12/09 3 0
15/13/10 4 1
16/14/09 400F
16/14/11 5 2
17/15/09 400
17/15/10 800F
17/15/12 6 3
18/16/10 800
18/16/11 1300F
18/16/13 7 4
19/17/11 1300 200
19/17/14 8 5
20/18/12 2000
20/18/13 4400F
20/18/15 9 6
21/19/13 4400 6300F
21/19/16 10
22/20/13 6300
23/21/14 15000
23/21/18 12
24/22/15 21000
25/23/17 100000

Viscosity Conversion Table

cSt to SUS Conversion Chart
cSt SUS cSt SUS
2.0 32.6 27.6 130.0
2.5 34.3 29.8 140.6
3.0 36.0 32.0 150.5
4.1 39.5 34.2 160.4
5.0 42.4 36.4 170.4
7.0 48.8 38.6 180.4
9.0 55.4 40.8 190.4
10.0 58.8 43.0 200.0
10.5 60.5 46.0 214.0
12.0 66.0 47.0 221
13.3 70.8 51.7 240.0
1.9 77.0 56.1 261.0
15.0 77.4 60.4 280.0
15.9 81.0 64.7 300.0
17.1 85.8 68.0 315.0
18.3 90.7 70.2 326.0
19.5 95.7 73.0 339.0
20.7 100.8 74.0 343.0
22.0 106.3 75.0 348.0
Note: The relationship between saybolt seconds and kinematic viscosities is linear above 75 cSt. To Convert Kinematic Viscosities above 75 cSt to SUS at 210’F, multiply by 4.664. To convert centistokes to SUS at 100’F, multiply by 4.632