There are many manufacturers of weight plates out there but very few offer calibrated plates. So what exactly is the difference between plates that are calibrated and those that are not? Firstly, calibrated plates are much more accurate in respect of the weight. Standard plates can be within around 2-4% accuracy of the stated weight. Whilst, this may not seem much at face value for, say, a 25kg plate. Consider a competitive powerlifter or strongman who may load 5 or 6 plates either side of a bar, this could result in a difference of + or – 12kg which is significant to say the least.
The act of calibrating something is to assess and adjust the precision and accuracy of something. So to calibrate a weightlifting plate is to ensure it is as close to the stated weight as possible meaning the weight tolerance is more likely to be in the region of 10’s of grams as opposed to 100’s of grams.
Secondly, calibrated plates have been produced with a specific hole diameter. The reason for this is to ensure the plates fit well on the bar without being either too tight or too loose. The correct diameter should be between 50.2mm and 52mm to ensure best fit onto most bars, although the ideal diameter of the centre hole should be 50.2-50.8 the International Powerlifting Federation rule book prefers a diameter of 52mm.
Do calibrated plates have to be certified? In short, no they don't. Plates that have been certified have been independently tested by federations, for example the International Powerlifting Federation, to verify their accuracy. This independent testing is costly and is a price that can be passed onto the customer making the plates much more expensive to purchase. If you want to invest in calibrated plates look for the tolerance specification when you shop around.
Why are calibrated plates more expensive than standard plates? Calibrated plates undergo much research and development. They take time to manufacture and cost significantly more than standard plates due to the processes involved and the attention to detail that needs to be taken on EVERY plate.
To purchase a set of calibrated plates means you are investing in plates that are significantly more accurate in terms of their weight, their hole diameter and which are produced with a much higher degree of skill.