Anatomic Structure

Generation

Number
per Generation

Mean
diameter
(m)

Mean
length
(m)

Cross-Sectional
Area
(m²× 10^-4)

Flow Rate

Reynolds Number
for Flow Rate
0.5 (L/s)

0.5 (L/s)

2.0 (L/s)

Velocity
(m/s)

Velocity
(m/s)

Trachea
Main Bronchi
Lobar Bronchi
Segmental Bronchi
Subsegmental Bronchi

0

1

0.01800

0.1200

2.54

1.9659

7.8635

1965.9

1

2

0.01220

0.0480

2.33

2.1397

8.5588

1450.2

2

4

0.00830

0.0190

2.13

2.3114

9.2458

1065.8

3

8

0.00560

0.0076

2.00

2.5388

10.1553

789.8

4

16

0.00450

0.0127

2.48

1.9659

7.8635

491.5

5

32

0.00350

0.0107

3.11

1.6249

6.4994

351.9

6

64

0.00280

0.0090

3.94

1.2694

5.0777

197.5

7

128

0.00230

0.0076

5.33

0.9407

3.7627

120.2

8

256

0.00186

0.0064

6.95

0.6892

2.7569

74.3

Terminal Bronchi
Bronchioles

9

512

0.00154

0.0054

9.53

0.5529

2.2116

44.8

10

1024

0.00130

0.0046

13.6

0.3681

1.4722

26.9

11

2048

0.00109

0.0039

19.1

0.2570

1.0281

15.5

12

4096

0.00095

0.0033

29.0

0.1723

0.6892

9.17

13

8192

0.00082

0.0027

43.2

0.1156

0.4625

5.12

14

16384

0.00074

0.0023

70.4

0.0710

0.2840

2.96

15

32768

0.00066

0.0020

112

0.0446

0.1785

1.62

Terminal Bronchioles
Respiratory Bronchioles
Alveolar Ducts
Alveolar Sacs

16

65536

0.00060

0.00165

185

0.0200

0.1080

0.670

17

131970

0.00054

0.00141

300

0.0167

0.0667

0.5

18

262144

0.00050

0.00117

534

0.0097

0.0389

0.260

19

524288

0.00047

0.00099

944

0.0055

0.0220

0.138

20

1489576

0.00045

0.00083

1600

0.0030

0.0120

0.078

21-23

15000000

0.00042

0.00060

~1400000

~0.0010

~0.0050

0.037-0.010

n-Generation Number;  L- Airway Length, (cm); A - Airway Cross-Sectional Area, (cm²)

Reference:   Weibel E.R. Morphometry of the human lung. New York. SpringerVerlag, Berlin Academic Press; 1963