# YOLOv3 Model Structure: Why is filters = (classes + coords + 1) * num?

Here's a tutorial about doing custom training of YOLO (Darknet): https://medium.com/@manivannan_data/how-to-train-yolov3-to-detect-custom-objects-ccbcafeb13d2

The tutorial guides how to set values in the .cfg files:

• classes = Number of classes, OK
• filters = (classes + 5) * 3

Why is it 'plus 5' then 'times 3'?

Some say it's (classes + coords + 1) * num, but I can't guess it out the meaning.

• 3 boxes per feature map and for every box you predict class probabilities + width + height + x + y + object confidence. – Brale Feb 27 '20 at 11:15
• uhm, and what is that 'coords'? – datdinhquoc Feb 28 '20 at 2:27
• well its x, y, height and width – Brale Feb 28 '20 at 8:57

filters = (classes + 5) * 3

filters = (classes + 5) * 3