thanks for the reply so im looking at about 8-10 kg of lead?A general rule of thumb will be 1kg of lead for each 10kg of body weight.
You may need a bit less with your surf suit as they tend to be a little less buoyant than an open cell suit of the same thickness.
Another thing to consider is how deep you dive. I use my full weighed belt when diving in areas of 0-15 m but have another lighter belt if I target areas where I will be diving deeper than 15 m.