Total Flow Area (TFA) is summation of nozzle areas which fluid can pass through a bit. When you consider about the TFA, you need to count all nozzles that you have in a bit or a reamer.

Basically, you can determine flow area with a simple circle area formula.

Flow Area = (π × D^{2}) ÷ 4

Where;

Area in square inch

π is a constant which approximately equates to 3.14159.

D is diameter in inch

Let’s make it easier for our life. Normally, a diameter of nozzle is reported in xx/32 inch. For example, a bit has 3 nozzles and each one of them has size of 20/32 inch.

The formula above can be simplified like this.

**Oilfield Unit**

Flow Area = N^{2} ÷ 1303.8

Where;

Flow Area for each nozzle in square inch

N is nozzle size in number/32 inch.

In order to find the total flow area of each bit or reamer, you must add all area of each nozzle.

**Example**

The bit that has a total of 5 nozzles. Three nozzles have a diameter of 10/32 inch and other 2 nozzles are 12/32 inch diameter.

Determine the total flow area (TFA) of the bit.

By the definition, you must sum every nozzle together in order to get the TFA; therefore, you can apply the formula above into this form.

Total Flow Area = (10^{2} + 10^{2} + 10^{2} + 12^{2} + 12^{2} )÷ 1303.8

Total flow area = 0.451 square inch

**Metric Unit**

Flow Area = N^{2} × π ÷ 4

Where;

Flow Area for each nozzle in square millimeter

N is nozzle size in millimeter .

**Example**

The bit that has a total of 5 nozzles. Three nozzles have a diameter of 7.94 mm and other 2 nozzles are 9.53 mm diameter.

Determine the total flow area (TFA) of the bit.

Total Flow Area = (7.94^{2} + 7.94^{2} + 7.94^{2} + 9.53^{2} + 9.53 ^{2} ) × π ÷ 4

Total flow area = 291 square mm

**Download Excel Spreadsheet for Total Flow Area Table in both oilfield and metric unit.**

**Ref books: **

Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.

Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.

Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.