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Calibration Weight Tolerances Explained

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What is Weight Tolerance

By raw definition, weight tolerance is the difference between the maximum and minimum values of a given nominal value. For applications in metrology, weight tolerance tells you how much deviation is allowed in the mass of your weight, while still being considered an accurate representation of that mass.

How to Determine Weight Tolerance

Weight tolerance is determined by the governing bodies that oversee national and international weighing standards. The three primary organizations are: ASTM International (Formerly the American Society for Testing and Materials), OIML (International Organization of Legal Metrology), and NIST (National Institute of Standards and Technology).

Each of these organizations have defined Calibration Weight Classes, which group weights based on how accurate they truly are to their nominal value.

High precision classes like ASTM Class 1 and OIML Class E1 will have very low tolerances, meaning the weight is as close to its true value as possible. Low precision classes like ASTM Class 6, OIML Class M2, or NIST Class F, will have a higher tolerance, meaning your weight is close to its reported mass, but may deviate a little more than a high precision class.

For example, let’s look at a 1 gram weight.

Class	Weight Tolerance	“In-Tolerance” Range
ASTM Class 1 (1 g weight)	0.034 mg	0.999966 g – 1.000034 g
ASTM Class 6 (1 g weight)	2.0 mg	0.998 g – 1.002 g

As we can see, the ASTM Class 1 weight tolerance is much more precise compared the Class 6. The tolerance range is much more narrow, indicating that the true mass of the Class 1 weight is much closer to a true gram than a Class 6.

The type of calibration weight class you should be using is determined by the class of your scale. For a full breakdown of scale classes, please refer to NIST Handbook 44 (Section 2) or OIML Handbook R76-1, (Section 3.2). You can also read our guide, What are Calibration Weight Classes, to learn more about scale/balance classes and calibration weight classes.

Scale Class vs. Calibration Weight Class Comparison Reference

Classification of Weighing Devices

Knowing your weight tolerance is an essential part of any weight calibration process. If your weight is not in tolerance, you run the risk of affecting your businesses’ processes, and worse, running afoul of federal compliance regulations which may govern your industry. That’s why it’s essential to keep your calibration weights in tolerance.

Weight Tolerance Chart Quick Reference

Weight Tolerance Chart

ASTM E617

Nominal Value	000	00	0	1	2	3	4	5	6	7
2000 kg					10 g	20 g	40 g	100 g	200 g	300 g
1000 kg					5	10	20	50	100	150
500 kg					2.5	5	10	25	50	75
300 kg					1.5	3	6	15	30	45
200 kg					1	2	4	10	20	30
100 kg					500 mg	1	2	5	10	15
50 kg	13 mg	25 mg	63 mg	125 mg	250	500 mg	1	2.5	5	7.5
30 kg	7.5	15	38	75	150	300	600 mg	1.5	3	4.5
25 kg	6.25	12.5	31	62	125	250	500	1.2	2.5	4.5
20 kg	5	10	25	50	100	200	400	1	2	3.8
10 kg	2.5	5	13	25	50	100	200	500 mg	1	2.2
5 kg	1.3	2.5	6	12	25	50	100	250	500 mg	1.4
3 kg	0.75	1.5	3.8	7.5	15	30	60	150	300	1
2 kg	0.5	1	2.5	5	10	20	40	100	200	750 mg
1 kg	0.25	0.5	1.3	2.5	5	10	20	50	100	550
500 g	0.13	0.25	0.6	1.2	2.5	5	10	30	50	300
300 g	0.075	0.15	0.38	0.75	1.5	3	6	20	30	210
200 g	0.05	0.1	0.25	0.5	1	2	4	15	20	160
100 g	0.025	0.05	.13	0.25	0.5	1	2	9	10	100
50 g	0.015	0.03	0.06	0.12	0.25	0.6	1.2	5.6	7	62
30 g	0.014	0.026	0.037	0.074	0.15	0.45	0.9	4	5	44
20 g	0.013	0.025	0.037	0.074	0.1	0.36	0.7	3	3	33
10 g	0.01	0.02	0.025	0.050	0.074	0.25	0.5	2	2	21
5 g	0.005	0.01	0.017	0.034	0.054	0.18	0.36	1.3	2	13
3 g	0.005	0.01	0.017	0.034	0.054	0.15	0.3	0.95	2	9.4
2 g	0.005	0.01	0.017	0.034	0.054	0.13	0.26	0.75	2	7
1 g	0.005	0.01	0.017	0.034	0.054	0.1	0.2	0.5	2	4.5
500 mg	0.002	0.003	0.005	0.01	0.025	0.08	0.16	0.38	1	3
300 mg	0.002	0.003	0.005	0.01	0.025	0.07	0.14	0.3	1	2.2
200 mg	0.002	0.003	0.005	0.01	0.025	0.06	0.12	0.26	1	1.8
100 mg	0.002	0.003	0.005	0.01	0.025	0.05	0.1	0.2	1	1.2
50 mg	0.002	0.003	0.005	0.01	0.014	0.042	0.085	0.16	0.5	0.88
30 mg	0.002	0.003	0.005	0.01	0.014	0.038	0.075	0.15	0.5	0.68
20 mg	0.002	0.003	0.005	0.01	0.014	0.035	0.07	0.12	0.5	0.56
10 mg	0.002	0.003	0.005	0.01	0.014	0.03	0.06	0.1	0.5	0.4
5 mg	0.002	0.003	0.005	0.01	0.014	0.028	0.055	0.08	0.2
3 mg	0.002	0.003	0.005	0.01	0.014	0.026	0.052	0.07	0.2
2 mg	0.002	0.003	0.005	0.01	0.014	0.025	0.05	0.06	0.2
1 mg	0.002	0.003	0.005	0.01	0.014	0.025	0.05	0.05	0.1
0.5 mg	0.002	0.003	0.005	0.01	0.014
0.2 mg	0.002	0.003	0.005	0.01	0.014
0.1 mg	0.002	0.003	0.005	0.01
0.05 mg	0.002	0.003	0.005	0.01

Weight Tolerance Chart

NIST Handbooks**

Nominal Value	105-1 F	44 Accept	44 Maint
2000 kg	200 g
1000 kg	100
500 kg	50
300 kg	30
200 kg	20
100 kg	10
50 kg	5
30 kg	3
25 kg	2.5
20 kg	2	750 mg	1500 mg
10 kg	1	500	1000
5 kg	0.5	400	800
3 kg	0.3	250	500
2 kg	0.2	200	400
1 kg	0.1	120	250
500 g	70 mg	88	175
300 g	60	75	150
200 g	40	50	100
100 g	20	35	70
50 g	10	20	40
30 g	6	15	30
20 g	4	10	20
10 g	2	8	12
5 g	1.5	5	10
3 g	1.3	4	8
2 g	1.1	3	6
1 g	0.9	2	4
500 mg	0.72	1.5	3
300 mg	0.61	1	2
200 mg	0.54	0.8	1.5
100 mg	0.43	0.5	1
50 mg	0.35	0.4	0.8
30 mg	0.3	0.3	0.6
20 mg	0.26	0.2	0.4
10 mg	0.21	0.15	0.3
5 mg	0.17	0.05	0.1
3 mg	0.14	.05	0.1
2 mg	0.12	0.05	0.1
1 mg	0.1	0.05	0.1

*NIST 105-1 Class F tolerances are rounded to two significant figures

Weight Tolerance Chart

OIML R-111

Nominal Value	Class E0*	E1	E2	F1	F2	M1	M2	M3
2000 kg				10 g	30 g	100 g	300 g	1000 g
1000 kg			1.6 g	5	16	50	160	500
500 kg			0.8	2.5	8	25	80	250
300 kg
200 kg			0.3	1	3	10	30	100
100 kg			160 mg	0.5	1.6	5	16	50
50 kg	12.5 mg	25 mg	80	250 mg	800 mg	2.5	8	25
30 kg
25 kg
20 kg	5	10	30	100	300	1	3	10
10 kg	2.5	5	16	50	160	500 mg	1.6	5
5 kg	1.3	2.5	8	25	80	250	800 mg	2.5
3 kg
2 kg	0.5	1	3.0	10	30	100	300	1
1 kg	0.25	0.5	1.6	5.0	16	50	160	500 mg
500 g	0.13	0.25	0.8	2.5	8	25	80	250
300 g
200 g	0.05	0.1	0.3	1	3	10	30	100
100 g	0.025	0.05	0.16	0.5	1.6	5	16	50
50 g	0.015	0.03	0.1	0.3	1	3	10	30
30 g
20 g	0.013	0.025	0.06	0.2	0.6	2	6	20
10 g	0.01	0.02	0.06	0.2	0.6	2	6	20
5 g	0.008	0.016	0.05	0.16	0.5	1.6	5	16
3 g
2 g	0.006	0.012	0.04	0.12	0.4	1.2	4	12
1 g	0.005	0.010	0.03	0.1	0.3	1	3	10
500 mg	0.004	0.008	0.025	0.08	0.25	0.8	2.5
300 mg
200 mg	0.003	0.006	0.02	0.06	0.2	0.6	2
100 mg	0.003	0.005	0.016	0.05	0.16	0.5	1.6
50 mg	0.002	0.004	0.012	0.04	0.12	0.4
30 mg
20 mg	0.002	0.003	0.01	0.03	0.1	0.3
10 mg	0.002	0.003	0.008	0.025	0.08	0.25
5 mg	0.002	0.003	0.006	0.02	0.06	0.2
3 mg
2 mg	0.002	0.003	0.006	0.02	0.06	0.2
1 mg	0.002	0.003	0.006
0.5 mg

* E0 is a theoretical tolerance that is 50% of OIML R 111 Class E1

Calibration Weight Tolerances Explained

What is Weight Tolerance

How to Determine Weight Tolerance

Scale Class vs. Calibration Weight Class Comparison Reference

Weight Tolerance Chart Quick Reference

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