Calibration -BRCGS version 9

Our sweet kitchen uses maximum weight for weighing raw material is 12 kgs. How many calibration reference weight we need and of what should be weight for reference weights. 

5 weights.

3 of them can guarantee the linearity of calibration graph. The extra two are spares for disregarding an outlier (if it appears) and determining the usage range.

The lightest calibration weight has to be equal or lighter than the smallest quantity you would measure.

For example, the product mass varies between 2kg to 10kg, 5 calibration points should be 1kg, 2kg, 5kg, 10kg and 12kg.

I think the previous answer is great practice.  You could probably get away with fewer weights but I agree by using 5, you can see if there is an outlier.

One thing to consider is what is the lightest weight you will weigh on the scales and the heaviest.  So if the lightest weight is 500g, I would use a lowest weight lighter than this and vice versa for the top end.

So for example to tweak the previous answer slightly, if your lightest weight is 500g and heaviest 12kg, I may use:

200g, 2kg, 5kg, 10kg, 15kg.

You could get away with 200g, 5kg, 15kg but would need to investigate (and take scales out of use) if any one of them was "out".

Also, an aside but too few people consider whether the scales they are using are the right ones for the accuracy needed.  One worth considering if you're weighing a very wide range on the same apparatus.