# How can I theoretically calculate how many circuit boards I can coat with my conformal coating material? It’s not easy to calculate how many PCBs you can coat with your conformal coating.

One of the simplest methods is to take a trial circuit board and weigh it before coating and after applying the coating. The difference in weight is the actual amount of conformal coating on the board. You then just need to know the solids content of the wet coating to calculate the real volume used.

However, this may not be practical.

If you want to make an estimate on paper then the following steps can help.

#### Theoretical estimate of conformal coating material used

The steps taken are as follows:

1. Calculate the surface area of the circuit board
2. Calculate the volume of the conformal coating material applied
3. Calculate the PCBs coated per millimeter
4. Calculate the PCBs coated per liter

This gives you a formula similar to below:

PCBs per liter = Solids content / Surface area x Thickness of dry film required x 1,000,000

Note: The key here is to check your units measured. In the example below, we use millimeters for board size.

Below is a worked example showing the above being used.

#### Theoretical example for conformal coating material use estimate

Here is an example to show the method. The key facts required are:

1. Board size to be completely covered: 100mm x 150mm
2. Thickness of dry film required: 25um (0.025mm)
3. Solids content of coating: 35%
4. Cost per liter: £20

Here the stages in full for ease of understanding:

###### Surface area of the board

Surface area = 100 x 150 mm

Surface area = 15,000 sq. mm’s

###### Volume of the coating material applied

Volume = Surface area x Thickness of dry film required

Volume = 15,000 x 0.025

Volume = = 375 cubic mm’s

###### PCBs coated per ml

PCBs coated per ml  = Solids content / Volume

PCBs coated per ml  = (35/100) / 375

PCBs coated per ml = 0.0009333 PCBs / ml

###### PCBs per liter

PCBs per liter = PCBs coated per ml x 1,000,000

PCBs per liter = 933.3 PCBs / liter

So, for a typical conformal coating applied on one side only on a flat board then approx. one thousand PCBs can be coated.

If you want to coat both sides of a board and allow for 3D coating on components then a more accurate result is to divide this number by 3.

So, for a typical conformal coating applied on both sides of a circuit then approx. 333 PCBs can be coated.

If you want to know what the price per board is you just divide the price for one liter by the number of boards per liter.

In this case, it would be approximately 6p per board.