Rated Capacity & Accuracy

Digital weigh scales come in various capacities- starting with jewelry scales (to weigh few grams) to weigh bridges (to weigh mining trucks weighing hundreds of tons). The maximum weight a scale can measure is called Rated Capacity.

Accuracy is an important characteristic of any measuring instrument. We have high, medium and low accuracy scales.

Low - kitchen scales and bathroom scales (non-commercial scales)
Medium - scales used for business purposes
High - scales used in labs or for scientific research

For commercial purposes accuracy is considered as 1/10000th of Rated Capacity. While jewelry scales measure grams with milligrams accuracy, weigh bridges weigh tons with kilograms accuracy. Example; accuracy of a 30T weigh bridge is ±5Kg. Accuracy defines the Least Count - the value with which the weight increments or decrements in the display.

Example 1; display value in a 10kg scale increments as shown below-
01.996 Kg
01.997 Kg
01.998 Kg
01.999 Kg
02.000 Kg

Example 2; value in a 30T weigh bridge increments as shown below-
20.080 T
20.085 T
20.090 T
20.095 T

Also there's another important parameter- Minimum Weight - the least possible weight that a scale can measure for the specified accuracy. It's not practical to measure 2kg on a 100kg scale or to weigh 200Kg on a 30T weigh bridge because we loose out on accuracy. It's ideal to use a 10Kg scale to weigh 2Kg and a 500Kg scale to weigh 200Kg. Minimum weight is normally considered 20 times Least Count.

Table below shows standard values of Least Count, Accuracy and Minimum Weight for some Rated Capacities.

Type of scale	Rated Capacity	Least Count	Accuracy	Minimum Weight
Laboratory	100g	0.01g	±0.01g	0.2g
Jewelry	500g	0.1g	±0.1g	2g
Table Top	10Kg	1g	±1g	20g
Bench	50Kg	5g	±5g	100g
Platform	100Kg	10g	±10g	200g
Floor	5000Kg	500g	±500g	10Kg
Weigh Bridge	30T	5Kg	±5Kg	100Kg
Weigh Bridge	100T	10Kg	±10Kg	200Kg

However scales with better accuracies are available. Naturally high accuracy scales would cost more than the standard ones.

'Dual Range' is another popular feature in jewelry, table-top, bench and platform scales. These scales measure lighter loads with high accuracy and switch over to lower accuracy for heavier loads.

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