How to Choose OIML Test Weights: Calibration Weight Classes (OIML R111 vs ASTM E617)
How to choose OIML test weights comes down to matching the weight class, from OIML E1 to M3 or ASTM Class 000 to 7, to your balance’s readability and your quality procedure. For a 0.1 mg balance, the A&D AD-200-20-2 Cal-Pal kit (200 g, 20 g and 2 g, with certificate) is on sale for $659.00 (regular $899.00), in stock.
Short answer: calibration weight classes tell you how close a weight is to its nominal value. In the US, laboratory weights follow ASTM E617 (Classes 000, 00, 0 and 1 through 7, tightest first), and internationally they follow OIML R111 (E1, E2, F1, F2, M1, M2, M3, tightest first). Field standards for heavy scales often follow NIST Handbook 105-1 Class F. For a 100 g weight, the maximum permissible error is 0.25 mg in ASTM Class 1, 0.16 mg in OIML E2 and 0.5 mg in OIML F1. Match the class to your balance’s readability and your quality procedure; the steps for choosing OIML test weights are below.
A calibration weight is only as useful as its tolerance. Put a weight that may be 2 mg off on a balance that reads 0.1 mg, and you have taught the balance the wrong answer. This guide explains the weight classes you will see on certificates and product pages, compares their tolerances, and shows which class fits which balance. MNM Scales is one of the largest scale distributors in the country, with over 30 years in business, and we stock ASTM Class 0 and Class 1 weights and sets with certificates.
ASTM E617 weight classes
ASTM E617 covers laboratory weights and precision mass standards in Classes 000, 00, 0, 1, 2, 3, 4, 5, 6 and 7. The lower the number, the tighter the maximum permissible error (formerly called tolerance). Classes 000 to 0 are reference standards for calibration labs and the most demanding analytical work; Class 1 is the usual choice for analytical and precision balances; Classes 2 to 4 suit precision toploaders and routine checks; and Classes 5 to 7 cover general and industrial use.
| Nominal | Class 0 | Class 1 | Class 2 | Class 3 | Class 4 |
|---|---|---|---|---|---|
| 1 g | 0.017 mg | 0.034 mg | 0.054 mg | 0.10 mg | 0.20 mg |
| 10 g | 0.025 mg | 0.050 mg | 0.074 mg | 0.25 mg | 0.50 mg |
| 50 g | 0.060 mg | 0.12 mg | 0.25 mg | 0.60 mg | 1.2 mg |
| 100 g | 0.13 mg | 0.25 mg | 0.50 mg | 1.0 mg | 2.0 mg |
| 200 g | 0.25 mg | 0.50 mg | 1.0 mg | 2.0 mg | 4.0 mg |
| 500 g | 0.60 mg | 1.2 mg | 2.5 mg | 5.0 mg | 10 mg |
| 1 kg | 1.3 mg | 2.5 mg | 5.0 mg | 10 mg | 20 mg |
| 2 kg | 2.5 mg | 5.0 mg | 10 mg | 20 mg | 40 mg |
| 5 kg | 6.0 mg | 12 mg | 25 mg | 50 mg | 100 mg |
Values are ± maximum permissible error in metric units, rounded to two significant figures.
OIML R111 weight classes
OIML R111 is the international recommendation for weights, used worldwide and common on European balances and in pharmaceutical quality systems. Its classes, from tightest to widest, are E1, E2, F1, F2, M1, M1-2, M2, M2-3 and M3. Under R111, the expanded uncertainty of each weight’s calibration must be no more than one-third of its maximum permissible error, and E1 and E2 weights are supplied with a calibration certificate.
| Nominal | E1 | E2 | F1 | F2 | M1 |
|---|---|---|---|---|---|
| 1 g | 0.010 mg | 0.03 mg | 0.10 mg | 0.3 mg | 1.0 mg |
| 10 g | 0.020 mg | 0.06 mg | 0.20 mg | 0.6 mg | 2.0 mg |
| 50 g | 0.03 mg | 0.10 mg | 0.3 mg | 1.0 mg | 3.0 mg |
| 100 g | 0.05 mg | 0.16 mg | 0.5 mg | 1.6 mg | 5.0 mg |
| 200 g | 0.10 mg | 0.3 mg | 1.0 mg | 3.0 mg | 10 mg |
| 500 g | 0.25 mg | 0.8 mg | 2.5 mg | 8.0 mg | 25 mg |
| 1 kg | 0.5 mg | 1.6 mg | 5.0 mg | 16 mg | 50 mg |
| 2 kg | 1.0 mg | 3.0 mg | 10 mg | 30 mg | 100 mg |
| 5 kg | 2.5 mg | 8.0 mg | 25 mg | 80 mg | 250 mg |
How to choose OIML test weights
OIML test weights are labelled by their R111 class. To choose them, work from the balance and the procedure, then check the maximum permissible error (MPE) at the nominal value you will use:
- Find the class your SOP, auditor or balance manufacturer names. European balance manuals and pharmaceutical procedures often give an OIML class, such as E2 for an analytical balance.
- Match the class to the balance. As a starting point, E1 suits mass labs and microbalances, E2 suits analytical balances that read 0.1 mg, F1 suits precision balances that read 1 mg, F2 suits toploaders that read 0.01 g, and M1 suits bench and industrial scales.
- Compare the MPE with the balance readability. Use the table above at the exact nominal value. At 100 g, E2 allows 0.16 mg, F1 allows 0.5 mg and F2 allows 1.6 mg.
- Ask for the certificate the procedure needs. An accredited calibration certificate gives the actual mass, the uncertainty and the density, which audited labs use.
- Compare ASTM E617 weights at the same value. If your procedure accepts ASTM weights, the MPE decides. An ASTM Class 1 100 g weight (0.25 mg) is tighter than OIML F1 (0.5 mg) at 100 g, and an ASTM Class 0 100 g weight (0.13 mg) is tighter than OIML E2 (0.16 mg).
Our calibration weights are ASTM classes with certificates, listed below with prices. For an OIML class requirement, call (832) 290-3120 or request a quote with the class, nominal values and certificate you need, and we will match the right weights.
NIST Class F: field standards for commercial scales
NIST Handbook 105-1 Class F weights are the field standards weights and measures officials and service companies use to test commercial scales, from bench scales to floor scales. A 1 kg Class F weight has a tolerance of 100 mg, which is tight enough for scales that read in grams or pounds. To find the tolerance the scale itself must meet when tested with those weights, use our Handbook 44 tolerance calculator. For how test weights are used on a floor scale, see how to calibrate a floor scale.
Commercial scales tested with Class F weights should be NTEP-certified models (see what NTEP means).
Texas note: TDA does not require an NTEP certificate for every device, but the scale must meet NIST Handbook 44 and suit its use; some scales do need one, so we recommend NTEP models and can check yours. See TDA’s scales used in trade guidance (PDF) and our TDA scale certification guide, or call us or TDA to confirm your use.
ASTM vs OIML: rough equivalents
| Typical use | ASTM E617 | OIML R111 |
|---|---|---|
| Calibration labs, microbalances | Class 000 to 0 | E1 |
| Analytical balances (0.1 mg) | Class 0 to 1 | E2 |
| Precision balances (1 mg) | Class 1 to 2 | E2 to F1 |
| Toploaders (0.01 g) | Class 2 to 4 | F1 to F2 |
| Bench and counting scales (0.1 g and up) | Class 4 to 6 | F2 to M1 |
| Industrial and floor scales | Class 6 to 7 or NIST Class F | M1 to M3 |
These pairings are typical starting points. The classes are not one-to-one; compare the actual maximum permissible error at the nominal value you need. Your SOP, auditor or the balance manufacturer may set a specific class.
How to choose between calibration weight classes
- Use the nominal value your balance asks for. Each balance accepts specific calibration masses; the A&D FX-120i, for example, accepts 100 g or 50 g.
- Use the class your procedure or manufacturer specifies. If none is set, compare the weight’s maximum permissible error with the balance readability and accuracy. For a 0.001 g balance calibrated at 100 g, ASTM Class 1 (0.25 mg) or OIML E2 (0.16 mg) is well inside one display digit (1 mg). Analytical balances usually call for ASTM Class 1 or better, or OIML E2.
- Decide on a certificate. Audited labs, pharmacies and legal-for-trade users usually need a calibration certificate. An accredited certificate lists the actual mass or correction, the measurement uncertainty, the assumed density and the environmental conditions.
- Plan to recertify. Weights wear and pick up contamination. Handle them with gloves or tweezers, store them in their case, and have them recalibrated on a schedule.
Calibration weights we stock
| Weight or set | Price | Class | Notes |
|---|---|---|---|
| A&D AD-5-500-1 set | $91.17 | ASTM Class 0 | 5 g, 500 mg and 1 mg, accredited calibration certificate |
| A&D AD-500-50-200 set | $136.05 | ASTM Class 1 | 500 g, 50 g and 200 mg, accredited calibration certificate |
| A&D AD-100-10-20 set | $659 | ASTM Class 1 | 100 g, 10 g and 20 mg, accredited calibration certificate |
| A&D AD-200-20-20 set | $659 | ASTM Class 1 | 200 g, 20 g and 20 mg, accredited calibration certificate |
| Rice Lake 50 g | $92.99 | ASTM Class 1 | Polished stainless steel, with case |
| Rice Lake 100 g | $108.99 | ASTM Class 1 | Polished stainless steel, with case |
| Rice Lake 200 g (12948) | $126.99 | ASTM Class 1 | Polished stainless steel, with case |
| MNM Scales 500 g | $249 | Class I | For 500 g calibration points |
| A&D 100 g | $59 | Class F | For the FX-120i and EJ-123; sold separately, not included with the balance |
Using your weight to calibrate a balance? See our step-by-step guides for the A&D FX-120i and the A&D EK-1200i.
Or let us calibrate it for you
MNM Scales calibrates scales and balances with in-house certificates (NIST-tested weights) or NIST calibration with a NIST-traceable certificate; see in-house vs NIST certificates and what calibration costs. We are TDA licensed with registered technicians, and nationwide mail-in calibration usually takes 1 to 3 business days. Choose the tier by your scale’s maximum capacity:
Up to 2.2 kg:
In-house calibration + certificate ($95) NIST calibration + NIST-traceable certificate ($395)
Over 2.2 kg up to 6.2 kg:
In-house calibration + certificate ($195) NIST calibration + NIST-traceable certificate ($495)
Over 6.2 kg up to 35 kg:
In-house calibration + certificate ($250) NIST calibration + NIST-traceable certificate ($595)
Over 35 kg up to 150 kg:
In-house calibration + certificate NIST calibration + NIST-traceable certificate
Floor and crane scales: Call (832) 290-3120 Request a quote
How often? Most businesses calibrate at least once a year; see how often to calibrate a scale.
Frequently asked questions
What are the calibration weight classes?
In the US, ASTM E617 defines Classes 000, 00, 0 and 1 through 7, with Class 000 the tightest. Internationally, OIML R111 defines E1, E2, F1, F2, M1, M1-2, M2, M2-3 and M3, with E1 the tightest. NIST Handbook 105-1 Class F covers field standards for testing commercial scales.
What are the classes of weights used in a laboratory?
Laboratories use ASTM E617 Classes 000 to 4 or OIML R111 classes E1, E2, F1 and F2. Analytical balances that read 0.1 mg usually use ASTM Class 1 or better, or OIML E2; precision balances and toploaders use ASTM Classes 1 to 4 or OIML F1 and F2.
How do I choose OIML test weights?
Use the class your procedure or balance manufacturer names. If none is set, compare the maximum permissible error at your nominal value with the balance readability: E2 for 0.1 mg analytical balances, F1 for 1 mg precision balances and F2 for 0.01 g toploaders.
What is the tolerance of a 100 g Class 1 weight?
An ASTM E617 Class 1 100 g weight has a maximum permissible error of plus or minus 0.25 mg. An OIML E2 100 g weight is 0.16 mg and an OIML F1 100 g weight is 0.5 mg.
Is ASTM Class 1 the same as OIML E2?
They are close but not identical. At 100 g, ASTM Class 1 allows 0.25 mg and OIML E2 allows 0.16 mg; at 1 kg, ASTM Class 1 allows 2.5 mg and E2 allows 1.6 mg. Compare the actual values for the mass you need.
What class of weight do I need for a 0.001 g balance?
For a 100 g calibration on a 0.001 g balance, ASTM Class 1 (0.25 mg) or OIML E2 (0.16 mg) is a common choice. Check your SOP or the balance manufacturer for a required class.
What does a weight calibration certificate show?
An accredited certificate lists the actual mass or the correction from nominal, the measurement uncertainty, the assumed density and the environmental conditions during calibration.
What is a NIST Class F weight?
Class F weights, defined in NIST Handbook 105-1, are field standards used to test commercial scales. A 1 kg Class F weight has a tolerance of 100 mg.