Culvert Sizing Calculator

Calculate the required culvert pipe diameter based on drainage area, rainfall, and slope. Compare corrugated metal, HDPE, and concrete pipe costs side by side.

Drainage Area (acres)

Rainfall Intensity (in/hr)

Runoff Coefficient (C)

Slope (%)

Pipe Length (ft)

Pricing (per linear foot, by material & size)

Size	Corrugated	HDPE	Concrete
12"	$8/ft	$12/ft	$18/ft
15"	$11/ft	$16/ft	$24/ft
18"	$15/ft	$22/ft	$30/ft
24"	$22/ft	$34/ft	$42/ft
30"	$32/ft	$48/ft	$58/ft
36"	$44/ft	$65/ft	$78/ft

Culvert Section

Design Flow (Q)

5.00 cfs

Q = 0.5 × 2 × 5

Required Size (Corrugated Metal)

18" diameter

5.7 cfs capacity

Best Value Total

$450.00

Corrugated Metal · 18" · 30 ft

Purchase Option	Quantity	Est. Cost
Corrugated Metal (18")Best value	5.7 cfs capacity	$450.00
HDPE Plastic (15")	7.0 cfs capacity	$480.00
Concrete (15")	6.5 cfs capacity	$720.00

Best value: Corrugated Metal at $450.00A 18" corrugated metal pipe provides 5.7 cfs capacity for a design flow of 5.00 cfs. At $15/ft for 30 ft, this is the most cost-effective option.

This calculator provides estimates using the rational method and Manning's equation for full-pipe flow. Actual sizing should account for inlet/outlet conditions, tailwater effects, and local design standards. Always consult a licensed engineer for final culvert design.