Posted: 20/03/2017 at 21:06
Fertilisers come in all different strengths so it's impossible to give you an accurate answer without knowing exactly what you have bought. There should be instructions on the pack though - don't be tempted to exceed the stated dose as you can easily do more harm than good.
If it is fish, blood and bone, that is quite forgiving and I would sprinkle about an ounce (25g) onto a large pot of the type typically used for trees and gently work it into the surface. Adding 2-3 cm of compost on top would do no harm, either.
If the dosage instructions are for an amount per square metre, dividing that by 3 or 4 would likely be about right.