Pipe Culverts: Circular Pipe Class

Table IA gives the class of circular reinforced concrete pipe required for culvert service, entered by nominal diameter and height of fill over the top of the pipe. Culvert tables run to greater cover than the corresponding storm sewer tables, because a culvert commonly sits under the full depth of a highway or railroad embankment rather than under a street section.

Reading Table IA

Columns are installation Types 1 through 7, each a band of fill height. Enter with the nominal diameter, move to the band covering the design cover, read the class. Roman numerals denote standard ASTM C 76 classes.

An asterisk marks a combination requiring special design. That notation is doing real work and should not be read as a footnote about availability. It means the tabulated selection has reached the edge of what a standard class covers — large diameter under deep fill — and the section must be designed for the actual loading, ordinarily as a D-load pipe under ASTM C 655, with the bedding and installation condition considered explicitly. Specifying "Class V" where the table shows an asterisked entry substitutes a nominal answer for a calculation.

Where the fill height comes from

Fill height is measured over the top of the pipe, not from the roadway centreline, and for a culvert crossing under a skewed or superelevated embankment the governing value is the maximum over the barrel, not the average. Two conditions deserve particular care:

Minimum cover. The shallow end of the range is governed by live load, not earth load, and construction loading is frequently more severe than the design traffic. A culvert that will be crossed by loaded haul equipment before the embankment is complete should be checked for that condition.
Deep fill. At the other extreme the installation condition dominates. Whether the pipe is in a trench, in a positive projecting embankment, or in an induced trench materially changes the earth load, and the tables assume a defined case.

Hydraulic sizing — which produces the diameter you enter the table with — is a separate exercise. Federal guidance is published as Hydraulic Design of Highway Culverts, which covers inlet and outlet control, performance curves and the entrance loss coefficients that decide which of the two governs.

English units

Pipe culverts, Table IA — class of circular reinforced concrete pipe by diameter and fill height (English units)
Nominal diameter, in	Type 1 — Fill Height: Greater than 1'- 0" Not exceeding 3'	Type 2 — Fill Height: Greater than 3' Not exceeding 10'	Type 3 — Fill Heights: Greater than 10' Not exceeding 15'	Type 4 — Fill Height: Greater than 15' Not exceeding 20'	Type 5 — Fill Height: Greater than 20' Not exceeding 25'	Type 6 — Fill Height: Greater than 25' Not exceeding 30'	Type 7 — Fill Height: Greater than 30' Not exceeding 35'
12	IV	II	III	IV	V	V	V
15	IV	II	III	IV	V	V	V
18	IV	II	III	IV	IV	V	V
21	IV	II	III	IV	IV	V	V
24	IV	II	III	IV	IV	V	V
30	IV	II	III	IV	IV	V	V
36	III	II	III	IV	IV	V	V
42	III	II	III	IV	IV	V	V
48	II	II	III	IV	IV	V	V
54	II	II	III	IV	IV	V	V
60	I	II	III	IV	V	V	V
66	I	II	III	IV	V	V	V
72	I	I	III	IV	V	V	V
78	I	I	III	IV	*V	*V	*V
84	I	I	III	IV	*V	*V	*V
90	I	I	III	*IV	*V	*V	*V
96	I	I	III	*IV	*V	*V	*V
102	I	I	III	*IV	*V	*V	*V
108	I	I	III	*IV	*V	*V	*V

Metric units

Pipe culverts — class of circular reinforced concrete pipe by diameter and fill height (metric units)
Nominal diameter, mm	Type 1 — Fill Height: Greater than 0.3 m Not exceeding 1 m	Type 2 — Fill Height: Greater than 1 m Not exceeding 3 m	Type 3 — Fill Heights: Greater than 3 m Not exceeding 4.5 m	Type 4 — Fill Height: Greater than 4.5 m Not exceeding 6 m	Type 5 — Fill Height: Greater than 6 m Not exceeding 7.5 m	Type 6 — Fill Height: Greater than 7.5 m Not exceeding 9 m	Type 7 — Fill Height: Greater than 9 m Not exceeding 10.5 m
300	IV	II	III	IV	V	V	V
375	IV	II	III	IV	V	V	V
450	IV	II	III	IV	IV	V	V
525	IV	II	III	IV	IV	V	V
600	IV	II	III	IV	IV	V	V
750	IV	II	III	IV	IV	V	V
825	IV	II	III	IV	IV	V	V
900	III	II	III	IV	IV	V	V
1050	III	II	III	IV	IV	V	V
1200	II	II	III	IV	IV	V	V
1350	II	II	III	IV	IV	V	V
1500	I	II	III	IV	V	V	V
1650	I	II	III	IV	V	V	V
1800	I	I	III	IV	V	V	V
1950	I	I	III	IV	*V	*V	*V
2100	I	I	III	IV	*V	*V	*V
2250	I	I	III	*IV	*V	*V	*V
2400	I	I	III	*IV	*V	*V	*V
2550	I	I	III	*IV	*V	*V	*V
2700	I	I	III	*IV	*V	*V	*V

Other shapes

Where vertical clearance rules out a circular section of the required capacity, the equivalent selection for horizontal elliptical and arch pipe is given in Table IIB, tabulated by equivalent round size with span, rise and minimum fill height. Precast box sections are covered under applicable specifications and box section dimensions.

Nominal diameter, in	Type 1 — Fill Height: Greater than 1'- 0" Not exceeding 3'	Type 2 — Fill Height: Greater than 3' Not exceeding 10'	Type 3 — Fill Heights: Greater than 10' Not exceeding 15'	Type 4 — Fill Height: Greater than 15' Not exceeding 20'	Type 5 — Fill Height: Greater than 20' Not exceeding 25'	Type 6 — Fill Height: Greater than 25' Not exceeding 30'	Type 7 — Fill Height: Greater than 30' Not exceeding 35'
12	IV	II	III	IV	V	V	V
15	IV	II	III	IV	V	V	V
18	IV	II	III	IV	IV	V	V
21	IV	II	III	IV	IV	V	V
24	IV	II	III	IV	IV	V	V
30	IV	II	III	IV	IV	V	V
36	III	II	III	IV	IV	V	V
42	III	II	III	IV	IV	V	V
48	II	II	III	IV	IV	V	V
54	II	II	III	IV	IV	V	V
60	I	II	III	IV	V	V	V
66	I	II	III	IV	V	V	V
72	I	I	III	IV	V	V	V
78	I	I	III	IV	*V	*V	*V
84	I	I	III	IV	*V	*V	*V
90	I	I	III	*IV	*V	*V	*V
96	I	I	III	*IV	*V	*V	*V
102	I	I	III	*IV	*V	*V	*V
108	I	I	III	*IV	*V	*V	*V

Nominal diameter, in	Type 1 — Fill Height: Greater than 1'- 0" Not exceeding 3'	Type 2 — Fill Height: Greater than 3' Not exceeding 10'	Type 3 — Fill Heights: Greater than 10' Not exceeding 15'	Type 4 — Fill Height: Greater than 15' Not exceeding 20'	Type 5 — Fill Height: Greater than 20' Not exceeding 25'	Type 6 — Fill Height: Greater than 25' Not exceeding 30'	Type 7 — Fill Height: Greater than 30' Not exceeding 35'
12	IV	II	III	IV	V	V	V
15	IV	II	III	IV	V	V	V
18	IV	II	III	IV	IV	V	V
21	IV	II	III	IV	IV	V	V
24	IV	II	III	IV	IV	V	V
30	IV	II	III	IV	IV	V	V
36	III	II	III	IV	IV	V	V
42	III	II	III	IV	IV	V	V
48	II	II	III	IV	IV	V	V
54	II	II	III	IV	IV	V	V
60	I	II	III	IV	V	V	V
66	I	II	III	IV	V	V	V
72	I	I	III	IV	V	V	V
78	I	I	III	IV	*V	*V	*V
84	I	I	III	IV	*V	*V	*V
90	I	I	III	*IV	*V	*V	*V
96	I	I	III	*IV	*V	*V	*V
102	I	I	III	*IV	*V	*V	*V
108	I	I	III	*IV	*V	*V	*V

Nominal diameter, in	Type 1 — Fill Height: Greater than 1'- 0" Not exceeding 3'	Type 2 — Fill Height: Greater than 3' Not exceeding 10'	Type 3 — Fill Heights: Greater than 10' Not exceeding 15'	Type 4 — Fill Height: Greater than 15' Not exceeding 20'	Type 5 — Fill Height: Greater than 20' Not exceeding 25'	Type 6 — Fill Height: Greater than 25' Not exceeding 30'	Type 7 — Fill Height: Greater than 30' Not exceeding 35'
12	IV	II	III	IV	V	V	V
15	IV	II	III	IV	V	V	V
18	IV	II	III	IV	IV	V	V
21	IV	II	III	IV	IV	V	V
24	IV	II	III	IV	IV	V	V
30	IV	II	III	IV	IV	V	V
36	III	II	III	IV	IV	V	V
42	III	II	III	IV	IV	V	V
48	II	II	III	IV	IV	V	V
54	II	II	III	IV	IV	V	V
60	I	II	III	IV	V	V	V
66	I	II	III	IV	V	V	V
72	I	I	III	IV	V	V	V
78	I	I	III	IV	*V	*V	*V
84	I	I	III	IV	*V	*V	*V
90	I	I	III	*IV	*V	*V	*V
96	I	I	III	*IV	*V	*V	*V
102	I	I	III	*IV	*V	*V	*V
108	I	I	III	*IV	*V	*V	*V