Paragon Pools — Weir & Vanishing Edge Calculator

1

Describe Your Edge

What effect do you want?

💧

Wetted Edge

~2 GPM/ft

🌊

Gentle Sheet

~5 GPM/ft

〰️

Laminar Flow

~13 GPM/ft

🏔️

Waterfall

~23 GPM/ft

Weir Length (ft)

Total length of the overflow/vanishing edge

Fall Height (ft)

Vertical drop: weir crest to catch basin water level

Construction Tolerance

⬇ Weir Flow Results

2

Pool Info (for Catch Basin Sizing)

Pool Surface Area (sq ft)

Max Bathers

Spa Volume (gal) — 0 if none

Only if spa drains into catch basin

⬇ Catch Basin / Surge Tank

⬇ Recommended Gutter & Drain Pipe

Weir Construction Guide

Reference Tables

Francis Weir Flow — GPM per Foot of Weir

Head (h)	GPM/ft	Typical Use
1/16″	0.6	Barely wet
1/8″	1.6	Wetted edge
3/16″	2.9	Wetted edge + tolerance
1/4″	4.5	Thin sheet
1/2″	12.7	Laminar flow
3/4″	23.4	Tumbling waterfall
1″	36.0	Heavy flow
1-1/2″	66.2
2″	102.0
3″	187.0

PVC Pipe Capacity — Flowing ½ Full (n=0.011)

Dia.	1%	2%	3%	4%
2″	10	14	17	20
3″	29	41	50	58
4″	61	87	106	122
6″	178	252	309	357
8″	381	539	660	762

Rectangular Channel Capacity — ½ Full (concrete n=0.013)

W × D	1%	2%
4″ × 4″	11	15
4″ × 6″	19	27
6″ × 6″	36	51
6″ × 8″	56	79
8″ × 8″	87	123
8″ × 12″	151	213
12″ × 12″	252	356

Francis Weir Formula: q = 36 × L × h^1.5
q = flow (GPM), L = weir length (ft), h = head over weir (inches).
For contracted weirs: subtract (0.3 × n × h^2.5) where n = 2.