Calculate drill bit total flow area (TFA) from nozzle sizes in 32nds of an inch, inches or mm, or find the equal nozzle size needed for a target TFA.

Add up to five nozzle sizes. For a 12/32-in nozzle, enter 12 or 12/32 with the 32nds unit.

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TFA Formula

The following formula is used to calculate the total flow area (TFA) of a downhole drilling tool when all nozzles have the same diameter.

TFA = ((π D2) / (4)) n
  • Where TFA is the total flow area (area units, e.g., in² or m²)
  • D is the diameter of each nozzle (length units, e.g., inches or meters)
  • n is the number of nozzles

To calculate total flow area (for identical nozzles), square the diameter, multiply by π/4, then multiply by the number of nozzles. If the tool has different nozzle diameters, compute each nozzle’s area and sum them.

Often for downhole drilling tools, nozzle diameters are expressed in 32nds of an inch (e.g., 10/32). For identical nozzles, the following is an approximation: its denominator 1303.8 is rounded from 4096/π. This calculator uses π directly.

TFA (in2)≈ n (S2) / (1303.8)
  • Where S is the nozzle size number in 32nds of an inch (so S = 10 for 10/32 in)
  • n is the number of nozzles (all the same size)

TFA Definition

What is TFA?

TFA stands for total flow area. It describes the combined area of openings through which fluid is intended to flow, commonly the nozzles of a downhole drilling tool. This calculator assumes circular openings; equal area alone does not establish equal flow rate or pressure loss.

Example Problem

How to calculate TFA?

First, determine the diameter of the nozzle. For this example, the diameter of the nozzle is found to be .45 inches.

Next, determine the number of nozzles per tool. In this example, there are 3 nozzles.

Finally, calculate the TFA using the formula above:

TFA = (π * D2) / 4 * n

TFA = (3.14159 * .452) / 4 * 3

TFA ≈ 0.4771 in². In reverse mode, enter a positive target area and the number of equal nozzles. The displayed nearest whole 32nd is a mathematical rounding comparison, not a product recommendation. Its area difference is rounded-size TFA minus target TFA; a rounded size of zero means no opening.