Checkweigher Compliance Requirements: NIST Handbook 133, FDA, USDA, and What an Inspection Actually Tests

A checkweigher on a production line is only as valuable as the compliance framework it is set up to satisfy. The machine itself — the conveyor, the weighing cell, the reject mechanism — is the hardware. The compliance framework is what determines the reject limits, the sampling requirements, the documentation trail, and whether your facility passes or fails a weights and measures inspection. Most production managers who operate checkweighers know how the machine works. Fewer understand the specific regulatory requirements that determine whether the data it produces is legally sufficient.

This article covers the complete checkweigher compliance framework for US manufacturers — NIST Handbook 133, NIST Handbook 44 Section 2.24, FDA and USDA net content regulations, the Maximum Allowable Variation (MAV) system, the two-rule compliance test, and what a weights and measures inspector is actually testing when they arrive at your facility.

The Regulatory Framework: Four Bodies, One Underlying Standard

Four federal agencies govern net content compliance for different product categories — but all of them reference the same underlying technical standard.

As confirmed by the 2026 edition of NIST Handbook 133 — the most current edition, incorporating amendments adopted at the NCWM 110th Annual Meeting in July 2025 — the federal agencies responsible for net content regulation are:

FDA (Food and Drug Administration): Regulates food, drugs, cosmetic products, tobacco, and medical devices under the Food, Drug, and Cosmetic Act (FDCA) and the Fair Packaging and Labeling Act (FPLA). FDA net content requirements for food are codified in 21 CFR Part 101.

USDA FSIS (Food Safety and Inspection Service): Regulates meat, poultry, and siluriform fish (catfish) products. USDA net content requirements are codified in 9 CFR Part 442, which incorporates NIST Handbook 44 by reference and adopts most of NIST Handbook 133’s sampling plans and MAV tables.

FTC (Federal Trade Commission): Regulates most non-food consumer packaged products under the Fair Packaging and Labeling Act. FTC applies NIST Handbook 133 methodology for net content verification.

EPA (Environmental Protection Agency): Regulates pesticides under FIFRA. EPA applies NIST Handbook 133 for pesticide net content compliance testing.

The common thread: As FSNS confirms, NIST Handbook 133 is the procedural guide used by all of these agencies — USDA, FDA, FTC, and EPA — to test whether packaged goods comply with net content labelling requirements. Understanding NIST Handbook 133 is understanding how every one of these agencies tests your product at inspection.

NIST Handbook 133: What It Is and Why It Governs Your Checkweigher Settings

NIST Handbook 133 is published by the National Institute of Standards and Technology and provides the standardized test procedures that weights and measures officials use when conducting compliance testing of packaged goods. The 2026 edition — the current edition — incorporates amendments adopted at the NCWM 110th Annual Meeting in July 2025.

The handbook establishes three things that directly determine how your checkweigher must be configured:

1. The Maximum Allowable Variation (MAV): The maximum permitted shortage for an individual package below its declared net weight. The MAV defines the reject threshold on your checkweigher — any package below the declared weight minus the MAV is an unreasonable shortage under the standard.

2. The sampling plans: Category A and Category B sampling plans that define the minimum sample size required for compliance testing of a lot, and the maximum number of individual packages within a sample that may exceed the MAV before the lot fails. These sampling plans are what an inspector uses to evaluate your lot — and they are what your own in-process sampling program should mirror.

3. The two-rule compliance test: The dual requirement that applies to every packaged goods compliance check — both the average weight and the individual package weight must comply simultaneously.

The Maximum Allowable Variation (MAV): The Number Your Checkweigher Reject Limit Must Satisfy

The MAV is the most practically important number in NIST Handbook 133 for checkweigher configuration. It defines the threshold below which a package is considered to have an unreasonable shortage — and it varies by declared net weight.

The following MAV values are taken from NIST Handbook 133 Table 2-5 for packages labeled by weight. This table applies to FDA-regulated food products and most consumer goods. USDA-regulated meat and poultry products use Table 2-9 — a separate table with different values.

MAV Table for Packages Labeled by Weight (NIST HB 133 Table 2-5 — FDA/FTC products):

How this applies to checkweigher reject limits:

A package declared at 16 oz (1 lb) has an MAV of 0.5 oz (1.5% of 1 lb = 0.24 oz under the weight-based calculation, but the table specifies 1.0 oz for packages at 1 lb). The checkweigher’s lower reject limit must be set at or above the declared weight minus the MAV — meaning any package below 15.0 oz triggers a reject.

The critical point for checkweigher configuration: Setting your reject limit exactly at the MAV boundary is legally compliant but operationally risky. A checkweigher’s measurement uncertainty — the statistical spread of its own readings at a given weight — means that packages very close to the MAV boundary will be inconsistently rejected across production runs. Industry best practice is to set the reject limit inside the MAV — typically at declared weight minus 50–75% of the MAV — creating a control buffer between the production process limit and the legal compliance limit.

The Two-Rule Compliance Test: Both Must Pass Simultaneously

This is the element of NIST Handbook 133 that most production managers understand incompletely. There are not one but two independent compliance requirements — and a production lot can fail either one independently.

Rule 1 — The Average Quantity Requirement: The average net weight of all packages in the sample must not be less than the declared net weight. If an inspector samples 30 packages from a lot and their average weight is 15.8 oz on a declared 16 oz product, the lot fails Rule 1 regardless of how few individual packages fell below the MAV.

Rule 2 — The Individual Package Requirement: No more than a defined number of packages in the sample may exceed the MAV (fall below declared weight minus MAV). The permitted number depends on the sampling plan — Category A or Category B — and the sample size. Exceeding this number fails Rule 2 regardless of the average weight.

As LegalClarity confirms, testing typically involves two main rules: the average weight of a group must be correct, and individual packages cannot be far below the labeled amount. A lot that passes one rule but fails the other is a non-compliant lot.

Why this matters for checkweigher configuration: A checkweigher that only controls average weight — through feedback to the filling machine — can pass Rule 1 while allowing individual packages to fail Rule 2. A checkweigher that only rejects individual outliers can produce a compliant package distribution while the line average drifts below target weight — passing Rule 2 while failing Rule 1. Complete compliance requires monitoring and controlling both simultaneously.

USDA FSIS Requirements: Different Rules for Meat and Poultry

USDA FSIS regulations under 9 CFR Part 442 impose requirements on checkweighers in meat and poultry plants that go beyond what FDA regulations specify for general food manufacturers.

Scale certification under NIST Handbook 44: As confirmed by 9 CFR Part 442, all scales used to determine the net weight of meat and poultry products in federally inspected establishments must meet NIST Handbook 44 requirements and display a valid certification from a state or local weights and measures authority, or have documented alternative testing procedures showing accuracy in accordance with NIST Handbook 44. This applies to checkweighers as automatic weighing instruments under NIST Handbook 44 Section 2.24.

USDA retain tags: If a USDA inspector places a “Retain” tag on a checkweigher or any other scale at a federally inspected establishment, that scale may not be used until it has been reinspected and retested by a USDA official, a state weights and measures official, or a state registered scale repair firm. The retain tag can only be removed by a USDA inspector. Operating a retained scale is a regulatory violation.

Separate MAV table for meat and poultry: USDA products use NIST Handbook 133 Table 2-9 — not Table 2-5 — for MAV determination. Table 2-9 includes specific provisions for different meat and poultry product groups and imposes tighter tolerances in some weight ranges than the general food MAV table. Any checkweigher operating in a USDA-inspected establishment must be configured against Table 2-9 values, not the general Table 2-5.

Wet tare procedures: USDA products subject to moisture loss — fresh meat, poultry with natural juices — have specific wet tare procedures defined in NIST Handbook 133. Checkweigher configurations for these products must account for moisture allowances when calculating compliance against the declared net weight.

NIST Handbook 44 Section 2.24: The Technical Standard for Automatic Checkweighers

While NIST Handbook 133 defines the compliance testing methodology, NIST Handbook 44 Section 2.24 is the technical standard that governs the checkweigher itself as an automatic weighing instrument.

Section 2.24 defines the accuracy, repeatability, and performance requirements that a checkweigher must demonstrate to be certified for legal-for-trade use. The key requirements include:

Minimum division value: The smallest increment the checkweigher can display and use for compliance determination. Section 2.24 specifies the minimum division value relative to the weighing range — a checkweigher with too coarse a division value cannot discriminate packages close to the MAV boundary accurately enough for legal-for-trade use.

Accuracy tolerance: The maximum permissible error at any point in the checkweigher’s operating range. This tolerance is what state Weights and Measures inspectors test when they evaluate a checkweigher in service. A checkweigher found outside tolerance during inspection must be removed from legal-for-trade service.

Influence factors: Section 2.24 defines the environmental conditions — temperature range, vibration, electromagnetic interference — under which the checkweigher must maintain accuracy. A checkweigher that meets accuracy requirements only under ideal conditions but drifts in the actual production environment is not compliant under Section 2.24.

NTEP certification: A checkweigher used for legal-for-trade net content determination must carry a valid NTEP Certificate of Conformance. As confirmed by the National Conference on Weights and Measures, NTEP certification confirms that the instrument type meets the requirements of NIST Handbook 44. A checkweigher without NTEP certification cannot be legally used to determine package compliance for commercial sale.

What a Weights and Measures Inspector Tests When They Arrive

Understanding what an inspector actually does at your facility prepares you for compliance and eliminates the most common sources of inspection failure.

Step 1 — Scale verification: The inspector verifies that every checkweigher and scale used in net content determination is NTEP certified, calibrated, and operating within NIST Handbook 44 tolerances. They will test the checkweigher’s accuracy at one or more weight points using certified test weights. A checkweigher that fails this test is condemned for legal-for-trade use immediately.

Step 2 — Lot sampling: The inspector selects a product lot — a production run of a specific product at a specific declared weight — and samples it using the Category A or Category B plan from NIST Handbook 133. For most lots, Category B sampling requires a minimum sample of 30 packages. The inspector weighs each package individually on a certified reference scale — not your checkweigher — and records the net weight of each package.

Step 3 — Tare determination: The inspector weighs the empty packaging of a representative sample of containers to establish the average tare weight. The net weight of each package is calculated as gross weight minus tare weight.

Step 4 — Two-rule evaluation: The inspector applies both the average quantity requirement and the individual package requirement to the sample. If either fails, the lot is non-compliant.

Step 5 — Documentation review: The inspector may request your checkweigher’s calibration records, your in-process weight data, your reject rate records, and your corrective action documentation. As FSNS confirms, facilities should establish a sampling program based on NIST Handbook 133. In-plant testing documentation demonstrates proactive compliance and is a significant factor in how an inspector assesses the seriousness of any findings.

Consequences of inspection failure:

• Notice of violation — formal written notice requiring corrective action
• Product seizure — non-compliant lot may be held or recalled
• Mandatory corrective action — written plan required before resuming production of the affected product
• Fines — penalties vary by state and agency; repeat violations carry escalating consequences
• Retailer consequences — major retailers increasingly require net content compliance documentation as a condition of supply. A regulatory finding affects the commercial relationship, not just the regulatory relationship.

How to Configure a Checkweigher for Compliance

Compliance-focused checkweigher configuration requires five elements working together.

1. Set reject limits inside the MAV — not at the MAV boundary: Determine the applicable MAV from NIST Handbook 133 Table 2-5 (FDA products) or Table 2-9 (USDA products). Set the lower reject limit at declared weight minus 50–75% of the MAV. This creates a production control buffer between your reject line and the legal compliance threshold.

2. Monitor both average and individual package weight: Configure the checkweigher’s statistical software to report the running batch average alongside individual package weights. Alert operators when the batch average approaches the declared weight — not just when individual packages approach the reject threshold.

3. Document everything automatically: Modern checkweighers produce individual package weight records, batch statistics, reject counts, and shift summaries. Configure the system to retain this data for at least 12 months — the typical period covered by an inspection sampling inquiry. For USDA-inspected establishments, retain records for the period required under 9 CFR Part 442.

4. Calibrate on a defined schedule: Checkweighers in legal-for-trade applications require formal calibration by an accredited service provider at defined intervals — typically quarterly for production lines running multiple shifts daily. Supplementary performance verification at shift start using certified test weights confirms calibration status between formal events. For the complete calibration requirements for industrial scales, including checkweighers, see our article on industrial scale calibration: how often and what compliance requires.

5. Maintain NTEP certification: Confirm that the checkweigher model carries a current NTEP Certificate of Conformance before purchasing to ensure legal-for-trade net content determination. Verify the CC number at NCWM’s NTEP database. A checkweigher without a current CC number cannot be legally used for this purpose.

For the full guide to how checkweighers work, the types available, and when an in-motion checkweigher is the right solution versus static spot-checking, see our article on what is a checkweigher and when do you need one.

FAQs

Conclusion

Checkweigher compliance is not a single regulatory requirement — it is the intersection of four agencies, two NIST Handbooks, and a two-rule compliance test that must be satisfied simultaneously on every lot.

Understanding NIST Handbook 133’s MAV tables and sampling plans tells you what your reject limits must satisfy and how an inspector will evaluate your product. Understanding NIST Handbook 44 Section 2.24 tells you what your checkweigher instrument must demonstrate to be legally used for that evaluation. Applying the two-rule test to your production data tells you whether your process is in compliance before an inspector arrives.

The facilities that consistently pass net content inspections are not the ones with the most sophisticated checkweighers. They are the ones whose reject limits are set correctly relative to the applicable MAV, whose calibration records are current, and whose in-plant testing program generates the documentation trail that demonstrates continuous compliance between inspections.