Floats will take a different amount of weight to set them correctly (i.e. just the coloured tip showing out of the surface of the water).
On the side of the float it will usually tell you how much shot is needed e.g. 4BB or 2.4g
|No. 10||0.03 g|
|No. 8||0.06 g|
|No. 4||0.2 g|
|No. 1||0.3 g|
Knowing the order of the shot sizes is important because 2 times one size is normally the weight of the next size (e.g. 2 No 10 = 1 No 8). This is useful when deciding how to shot a float.
You might want most of the weight around the float and a couple of small shot further down the line, so a 4BB Float would be shotted with 3 BB + 1 No.4 around the float to lock it in place then 1 No. 6 and 2 No. 8 shot spread equally down the line.
1 No. 4 + 1 No. 6 + 2 No. 8 = 1 BB so the total is 4 BB.