What is the English word for the stones used in Indian weighing balance?

Solution 1:

They are called "scale weights" or just "weights". You have a 1kg weight, a 500g weight, and so on.

Solution 2:

These are termed calibration weights (also reference weights) as illustrated and described here.

They are usually sold in sets, enclosed in a felt-lined box supplied with tweezers so as to avoid disturbing the calibrated weight by getting fingerprints on the weights.

Calibration weights are known masses such as a 100g or 500g weight.

Solution 3:

The word you are looking for is "masses" or "standard masses." This is what is placed in one pan (or scale) of a balance. Since there are two pans, they are collectively known as "scales."

"Masses" is not only more traditional, but also more precise: after all, since you are preforming your measurement in a constant gravitational field using a comparison, you are indeed measuring the mass and not just the weight of the object.