Online Calculators

Calculate Faircloth Skimmer® Size & Print Detail Drawing

Use the following calculator to create a detail drawing in PDF format. You can then print or save the PDF document. Note: You can calculate multiple skimmers — simply click “Add Row” to add another details for each additional skimmer.


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Calculate Faircloth Skimmer® Size



The required basin volume is the actual volume you intend to drain, not the provided or total volume which is often larger. If a pool of water is to be maintained between storms, do not include that volume. Number of Days to drain is usually determined by local or state regulations. Where there is no requirement 3 days is recommended. Keep in mind the quicker the basin is to drain the larger the skimmer required. In NC, assume 3 days to drain.
Skimmer Size

0 inches

Orifice Radius

0 inches

Orifice Diameter

0 inches

Basin Volume Calculator

If you do not know the basin’s volume but you do know the dimensions and depth of a square or rectangular basin, use this calculator to estimate the volume.

Length Width
Top of water surface in feet
Bottom dimensions in feet
Depth in feet
Estimated Basin Volume

0 cubic feet

Important!

The calculator does not take into consideration Common Sense. For example, if the volume entered is even one cubic foot greater that the maximum calculated capacity of a skimmer the next larger size will be given as the answer.

In reality, a reasonable judgment would be that the smaller size is adequate given the room for error in the assumptions that go along with the design and sizing process.

For example: using the entire volume of the basin to determine the skimmer size assumes that the basin fills during every rain event, which is usually not the case (therefore, the basin will drain somewhat quicker); it also assumes inflow to the basin stops when the basin is full, which may not be the case (inflow may continue, lengthening the drain time); or another rain event may occur before the basin drains.

Therefore it is recommended that the following flow capacities chart be used together with the calculator.

FLOW CAPACITIES (in ft 3 ) FOR THE Faircloth Skimmer®

Skimmer size 1.5″ 2″ 2.5″ 3″ 4″ 5″ 6″ 8″
24 hours 1,728 3,283 6,234 9,774 20,109 32,832 51,840 97,978
2 day 3,456 6,566 12,468 19,548 40,218 65,664 103,680 195,956
3 day 5,184 9,849 18,702 29,322 60,327 98,496 155,520 293,934
4 day 6,912 13,132 24,936 39,096 80,436 131,328 207,360 391,912
5 day 8,640 16,415 31,170 48,870 100,545 164,160 259,200 489,890
6 day 10,368 19,698 37,404 58,644 120,654 196,992 311,040 587,868
7 day 12,096 22,981 43,638 68,418 140,763 229,824 362,880 685,846

DETERMINING SKIMMER SIZE

  • Eight sizes available, ranging from 1½” for small sediment traps to 8” for very large basins.
  • Size refers to the maximum diameter of the inlet.  For example, a 4” Faircloth Skimmer® has a 4” maximum orifice size.
  • Each Faircloth Skimmer® includes a plug and adjustable cutter for making an orifice (hole) smaller than the inlet to customize the flow rate for the particular basin.

Method Used

The flow rates used in the calculator and listed in the chart are theoretical rates calculated using the orifice equation and the head on the inlet for each size skimmer. (Note that the head is different for each size skimmer.)

Also, the head may vary slightly when the skimmer is in use, plus or minus, depending upon the depth of water and the position of the skimmer. The actual flow rate for the installed skimmer may be slightly less than calculated, especially when the barrel has a flat or low slope.

Any variation in flow rate is considered insignificant enough to appreciably affect the drain time considering the number of variables involved. Therefore, the theoretical rates are used to simplify the orifice sizing process.

The calculation is rounded to the nearest 10th of an inch because that is as close as the cutter can be adjusted and the orifice cut.