An NRCS inspector takes packs of your 500 g peanuts from a supermarket shelf, and a few weeks later you are asked for your weight-control records. One light pack is not the problem. The problem is whether you can show that the whole lot met South Africa’s average weight rules, and that your checkweigher really removed the packs it should have.
South Africa’s average weight rules, set by SANS 458 through GN R877 of 2018, judge the lot, not a single pack: the mean must be at least the nominal quantity, no more than 2.5 % of packs may be short by more than the tolerable deficiency T, and no pack may be short by more than 2T.
The QC Inspector Course for Food and Beverage Manufacturing teaches the SANS 458 rules, fill targets, checkweigher verification and control charts by filler head, with a free net content checker: about 20 hours online, R2 950.
Average weight rules in South Africa: the key facts
| Parent law | Legal Metrology Act 9 of 2014 |
|---|---|
| Regulations | GN R877 of 24 August 2018 (GG 41854), the Legal Metrology Regulations |
| Marking and temperature | Reg 20: marking per SANS 289. Reg 23: 20 °C standard temperature for liquids |
| Instruments and tolerances | Regs 31 and 32: SANS 458, “Tolerances permitted for the accuracy of measurements made in terms of legal metrology legislation” |
| Quantity mark | Reg 35: the “e” mark as defined in SANS 1841; registered companies only; 5-year registration (reg 37) |
| Measurement mark | Reg 36: the reversed epsilon, per SANS 1840. Reg 38: offences for unauthorised use of the marks |
| The three rules | Mean at least the nominal quantity; no more than 2.5 % of packs are T1 errors; no pack is a T2 error |
| Enforced by | NRCS Legal Metrology |
| Official reference test | The OIML R87 official reference plan (lots 600–100 000): 98 packs, up to 5 T1 packs. Not a packer QC plan |
What are the three average-quantity rules?
Rule 1: the mean of the lot is at least the nominal quantity. Rule 2: no more than 2.5 % of packs are T1 errors, short by more than T but not more than 2T. Rule 3: no pack is a T2 error, short by more than 2T. T is the tolerable deficiency SANS 458 sets for each nominal quantity.
This is the average system, and it is why one pack under the declared weight is not, by itself, illegal. Fillers vary, so the rules allow some packs below nominal as long as the lot delivers what the label says and no pack is badly short. T is also widely called the tolerable negative error (TNE). OIML R87 treats T1 and T2 as separate bands, so a T2 pack is not also counted as T1.
How do you calculate T, T1 and T2?
Look up T for the nominal quantity in the SANS 458 table, which matches OIML R87:2016: for example, 3 % for 300 to 500 g and 15 g for 500 to 1,000 g. The T1 limit is nominal minus T; the T2 limit is nominal minus 2T. A 500 g pack has limits of 485 g and 470 g.
| Nominal quantity Qn (g or ml) | T |
|---|---|
| 0 to 50 | 9 % of Qn |
| 50 to 100 | 4.5 g or ml |
| 100 to 200 | 4.5 % of Qn |
| 200 to 300 | 9 g or ml |
| 300 to 500 | 3 % of Qn |
| 500 to 1,000 | 15 g or ml |
| 1,000 to 10,000 | 1.5 % of Qn |
| 10,000 to 15,000 | 150 g or ml |
| Above 15,000 | 1 % of Qn |
| Pack | T | T1 limit and T2 limit |
|---|---|---|
| 30 g snack | 9 % × 30 = 2.7 g | 27.3 g and 24.6 g |
| 340 g can | 3 % × 340 = 10.2 g | 329.8 g and 319.6 g |
| 500 g peanuts | 15 g | 485 g and 470 g |
| 2 L cola | 1.5 % × 2,000 = 30 ml | 1,970 ml and 1,940 ml |
Always weigh net: film, glass and cans vary, so sample the tare from the same run or weigh each pack’s own packaging. Products sold by volume are checked by mass using the density at 20 °C: at 1.040 g/ml, a 2 L cola has a nominal 2,080.0 g net and a T1 limit of 2,048.8 g.
Who may use the e-mark?
Only a registered packer. GN R877 reg 35 defines the quantity mark as the “e” mark in SANS 1841, for registered companies only, with registration for five years (reg 37). Unauthorised use of the mark is an offence under reg 38. A packer using the e-mark must run a documented quantity-control system: records, check frequencies and suitable equipment.
SANS 1841 is the standard for the packer’s own system, so write your weight-control task card from the standard itself, not from a summary. Reg 31 requires suitable measuring instruments in terms of SANS 458, and an inspector will expect to see them and their records.
How do you set a fill target without giving product away?
Work out three minimum targets and use the largest: the nominal quantity Qn; Qn − T + 2σ; and Qn − 2T + 3.09σ, where σ is the filler’s standard deviation. Then add a margin for drift. A tight filler is usually governed by rule 1; a variable one by rule 2, and it pays in give-away.
The 2σ term keeps about 2.3 % of packs below the T1 limit, inside the 2.5 % allowance; the 3.09σ term keeps about 1 pack in 1,000 below the T2 limit. A 500 g pack on two fillers:
| Rule and minimum target | Tight filler, σ 2.5 g | Variable filler, σ 10 g |
|---|---|---|
| Rule 1: Qn | 500 g | 500 g |
| Rule 2: Qn − T + 2σ | 485 + 5 = 490 g | 485 + 20 = 505 g |
| Rule 3: Qn − 2T + 3.09σ | 470 + 7.7 = 477.7 g | 470 + 30.9 = 500.9 g |
| Governing target | Rule 1: about 500.5 to 501 g | Rule 2: about 505 g plus a margin |
Four extra grams a pack on a million packs is four tonnes of product given away. The common mistake is setting every target at “nominal plus two standard deviations”: on the tight filler that means 505 g where about 501 g would do. Try your own figures in the free Net Content and Weight Control Calculator.
How do you verify a checkweigher?
Prove two things at start-up, at every changeover, at the end of the run and at set intervals between: that it weighs correctly, and that the reject really removes a light pack. Run a certified pack at target weight and one just below the reject threshold, leading and trailing, and check the light pack lands in a locked bin.
- Threshold: at or above Qn − T, plus a margin for the checkweigher’s dynamic variation. For 500 g: 485.0 g plus 2.0 g gives 487.0 g.
- Test packs: confirmed on a verified bench scale first; for that line, 501.0 g must pass and 486.0 g must be rejected every time.
- Frequency: every 2 to 4 hours between start-up and end of run is typical practice.
- If it fails: stop the line and hold everything since the last good check, including cased stock, then re-weigh it once the checkweigher passes.
The bench scale needs its own routine: a sensitivity check every shift, and repeatability, eccentricity and linearity checks at set intervals, with test weights made to OIML R111.
Worked example: a 500 g peanut line
At 16:40 on Thursday 5 November 2026, Ayanda Mthembu, B-shift QC inspector at Isipho Beverages & Snacks in Hammarsdale (the fictional factory in ASC’s Course 2), weighs 10 packs of 500 g peanuts from the end of line S2. One reads 468.0 g net. Every pack on S2 crosses a checkweigher.
Step 1: Classify the pack
T is 15 g, so the T2 limit is 470 g. At 468.0 g the pack is short by 32 g, more than 2T: a T2 error, which no lot may contain.
Step 2: Find out how it passed the checkweigher
The screen shows a threshold of 465.0 g, an old trial value left in the recipe at the 14:00 changeover. It should read 487.0 g.
Step 3: Find the last good check
The 14:15 start-up verification used only the target-weight pack. That proved weighing, not rejecting, so the last good check was before the changeover.
Step 4: Hold
Ayanda stops the line and holds every 500 g pack made since 14:00, including those in cases and on the pallet.
Step 5: Fix and verify
Bongani Cele, the engineer, resets the threshold to 487.0 g. Ayanda runs the 501.0 g and 486.0 g test packs, leading and trailing: the light pack lands in the locked bin every time and the count matches.
Step 6: Re-weigh and release
The held packs go back through the checkweigher. Priya Naidoo, the QA manager, releases them only when the record shows the three rules are met.
Step 7: Close the cause
The corrective action sits in change control, not retraining: any recipe change on a checkweigher now needs a verification with both test packs before restart.
Check your own lines with the free Net Content and Weight Control Calculator, then learn the full weight-control job in Course 2, including X-bar/R charts by filler head: R2 950, about 20 hours.
What does an NRCS inspector actually ask for?
An NRCS Legal Metrology inspector wants evidence that each lot met the three rules before it left: weight-control records by filler head, the tare method, verified scales and checkweighers with their test records, density at 20 °C for liquids sold by volume and, if you use the e-mark, your SANS 1841 registration.
- Show me the weight-control record for this batch: time, head, tare, net weights, mean, and T1 and T2 counts.
- How was the tare established: average or individual?
- Show me the scale check records and test-weight certificates.
- Show me the checkweigher verification: test packs, proof of reject and bin reconciliation.
- How was the fill target set, and who approved it?
- If the pack carries an “e”, show me the registration certificate.
Inspectors use a different plan from yours. The OIML R87 official reference plan (lots 600–100 000) takes 98 packs and allows up to 5 T1 packs, giving the lot the benefit of sampling error. It is not a packer QC plan: the NRCS brochure says official plans are “not recommended for use in the quantity control processes of the packer”.
Frequently asked questions
How much can a pre-packed product be underweight in South Africa?
A pack may be short by up to T without being an error, and up to 2.5 % of packs may be short by more than T but not more than 2T, as long as the lot’s mean is at least the nominal quantity. No pack may be short by more than 2T. For 500 g, T is 15 g.
What is the tolerable negative error?
Another name for T, the tolerable deficiency set for each nominal quantity in SANS 458 and OIML R87:2016: for example 3 % for 300 to 500 g, 15 g for 500 to 1,000 g and 1.5 % for 1,000 to 10,000 g or ml.
Is one pack under the declared weight illegal?
No. The rules judge the lot. A pack below nominal is allowed if it is short by no more than T, and a few T1 packs are allowed within 2.5 %. A T2 pack, or a lot whose mean is below nominal, is never allowed.
How are drinks sold by volume checked?
By mass, converted with the product’s density at 20 °C, the standard temperature in GN R877 reg 23. For carbonated drinks, measure density on degassed product.
Does SANS 458 round T the same way as OIML R87?
OIML R87 rounds T up to the next 0.1 g or ml for nominal quantities up to 1,000 g or ml. We could not confirm that SANS 458 uses the same rounding, so check your copy. The 340 g, 500 g, 30 g and 2 L examples above are unaffected.
Who enforces the average weight rules?
NRCS Legal Metrology, under the Legal Metrology Act 9 of 2014 and GN R877 of 2018. Retail customers also look at their suppliers’ weight-control records during supplier audits.
Fill to the rules, not to the scale
Weight control is one of the few QC jobs where the law, the customer and finance read the same record.
QC Inspector Course for Food and Beverage Manufacturing: Course 2 of the FS60 series, 8 modules, about 20 hours, self-paced.
- R2 950, no VAT charged; after Course 1 or at least 12 months in food production, QC or a food lab
- Three practice tools: Net Content and Weight Control Calculator and AQL Sampling Plan Calculator (both free to try) and the Line QC Check Sheet Builder
- A video-proctored final exam: 40 questions from a bank of 90, 75 minutes, calculator allowed, 75 % to pass, 2 attempts
- A QR verified Certificate of Achievement an employer or auditor can check
- ASC Food Safety Training is a FoodBev SETA accredited training provider (587/00337/1900); the FS60 courses are non-credit-bearing short courses
Sampling incoming lots too? Read ISO 2859-1:2026 changes and AQL sampling explained. Compare levels on the food quality control training page, see all courses or contact us about a team of five or more.
Last reviewed: 28 September 2026.
Sources: GN R877 of 24 August 2018 (GG 41854); OIML R87:2016, Quantity of product in prepackages; NRCS Legal Metrology brochure (SANS 458 Table 1); SANS 458, 289, 1840 and 1841 (SABS).