AQL Calculator for Phone Inspections: How to Use It
How AQL (Acceptable Quality Level) works in practice for pre-shipment phone inspections — sample sizes, defect classification, and pass/fail thresholds.
AQL sampling tables (ISO 2859-1) determine how many units to inspect from a lot. At AQL 1.5 under general inspection level II: a 500-unit lot requires inspecting 80 phones, with a pass threshold of 3 or fewer major defects; a 1,200-unit lot requires 125 inspections, pass if 5 or fewer major defects. Critical defects carry a zero-tolerance threshold — a single critical defect fails the entire lot.
What Is AQL (Acceptable Quality Level)?
AQL — Acceptable Quality Level — is the maximum percentage of defective units a buyer is willing to tolerate in a shipment. It is not a pass rate; it is a defect ceiling. If the sampled defects fall at or below the AQL threshold, the lot passes. If they exceed it, the lot is rejected.
AQL is the universal language of pre-shipment inspection. Every third-party inspection firm — QIMA, Bureau Veritas, Intertek, local HK and Shenzhen inspection houses — uses the same underlying standard: ISO 2859-1 (formerly MIL-STD-105E). When a supplier quotes “AQL 2.5,” they are referencing a specific, internationally defined tolerance level under that standard.
The ISO 2859-1 Standard
ISO 2859-1 governs sampling inspection by attributes. It specifies:
- How many units to pull from a lot (sample size) based on lot size and inspection level
- How many defects — across severity classes — trigger a rejection
The standard defines three general inspection levels: Level I (reduced scrutiny), Level II (normal — the default for most phone trades), and Level III (tightened scrutiny). Level II is used unless there is a documented reason to deviate.
AQL Levels Used in Phone Trade
| AQL Level | Meaning | Typical Application |
|---|---|---|
| 1.0 | Max 1 defect per 100 units accepted | Critical defects; high-value flagship stock |
| 2.5 | Max 2.5 defects per 100 units accepted | Major defects; standard for used/refurbished lots |
| 4.0 | Max 4 defects per 100 units accepted | Minor/cosmetic defects; acceptable cosmetic tolerance |
The most common configuration in the wholesale phone trade is AQL 1.0 for critical, 2.5 for major, 4.0 for minor — applied simultaneously in a single inspection.
How Defects Are Classified for Phone Inspections
All defects must be classified before the inspection, agreed with the inspector, and documented in the inspection criteria sheet.
| Class | Definition | Phone Examples |
|---|---|---|
| Critical | Unit is non-functional or unsafe | Dead on arrival, no power, cracked display glass rendering touch dead, swollen battery |
| Major | Functional but significantly impaired or visibly defective in a way that affects resale | Screen burn, ghost touch, broken charging port, Face ID/fingerprint failure, severely damaged housing |
| Minor | Cosmetic flaw that does not affect function or resale grade | Light scratches within grade tolerance, minor scuffs on bezel, faint screen marks within stated grade |
Classification is grading-dependent. A crack classified as “minor” on C-grade stock would be “major” on A-grade stock. The inspection criteria sheet must reference the agreed cosmetic grade.
AQL Reference Table — Sample Sizes by Lot Size (Level II)
This table is derived from ISO 2859-1 Table 1 and Table 2-A. “Ac” = Accept number; “Re” = Reject number.
| Lot Size | Sample Size | AQL 1.0 Ac/Re | AQL 2.5 Ac/Re | AQL 4.0 Ac/Re |
|---|---|---|---|---|
| 2–8 | 2 | 0/1 | 0/1 | 0/1 |
| 9–15 | 3 | 0/1 | 0/1 | 0/1 |
| 16–25 | 5 | 0/1 | 0/1 | 0/1 |
| 26–50 | 8 | 0/1 | 0/1 | 0/1 |
| 51–90 | 13 | 0/1 | 0/1 | 1/2 |
| 91–150 | 20 | 0/1 | 1/2 | 1/2 |
| 151–280 | 32 | 0/1 | 1/2 | 2/3 |
| 281–500 | 50 | 0/1 | 3/4 | 5/6 |
| 501–1200 | 80 | 0/1 | 5/6 | 7/8 |
| 1201–3200 | 125 | 1/2 | 7/8 | 10/11 |
| 3201–10000 | 200 | 3/4 | 10/11 | 14/15 |
| 10001–35000 | 315 | 5/6 | 14/15 | 21/22 |
Use arrows in the full ISO table if a cell shows a letter code rather than a number — follow the arrow to the nearest defined sample size.
Worked Example: 500-Unit Lot at AQL 2.5, Level II
A buyer in Lagos is sourcing 500 refurbished iPhone 12 units from a Shenzhen trader. The agreed inspection criteria:
- Critical AQL: 1.0
- Major AQL: 2.5
- Minor AQL: 4.0
- Inspection level: II
Step 1 — Find the sample size. Lot size 500 falls in the 281–500 range. Sample size = 50 units.
Step 2 — Pull the sample. The inspector randomly selects 50 units from across the lot (not just top-of-pallet). Randomness is essential — sequential or top-pallet-only pulls are a common manipulation.
Step 3 — Inspect and classify defects. Inspector finds: 0 critical defects, 3 major defects, 4 minor defects.
Step 4 — Apply accept/reject numbers. From the table, for a 50-unit sample:
| Class | Found | Ac | Re | Result |
|---|---|---|---|---|
| Critical (AQL 1.0) | 0 | 0 | 1 | PASS |
| Major (AQL 2.5) | 3 | 3 | 4 | PASS |
| Minor (AQL 4.0) | 4 | 5 | 6 | PASS |
The lot passes on all three counts. If major defects had been 4 or more, the lot would be rejected.
Step 5 — Issue the inspection report. A passing result does not guarantee zero defects in the full lot. It means the defect rate in the sample was within the agreed statistical tolerance. The buyer should factor the AQL level into their downstream sorting and returns allowance.
When to Use AQL Sampling vs. 100% Inspection
| Situation | Recommended Approach |
|---|---|
| Large lots (100+ units) at standard cosmetic grades | AQL sampling, Level II |
| High-value flagship devices (e.g., iPhone 15 Pro, Samsung S24 Ultra) | 100% inspection — justified by unit economics |
| Lots with a known quality history problem from the supplier | 100% inspection or Level III AQL |
| First order from a new supplier | 100% inspection or tightened Level III AQL |
| Repeat supplier with documented passing history | Level I (reduced) may be acceptable |
| Components and accessories (cables, batteries) | AQL sampling appropriate; critical AQL 1.0 for batteries |
100% inspection is standard practice for high-value lots in the HK and Shenzhen inspection market, even though it costs more. On a 500-unit lot of premium flagships, the per-unit inspection cost is trivial relative to the margin risk of accepting a bad lot.
Using an AQL Calculator
Online AQL calculators (QIMA, Inspectorio, and standalone tools) automate the lookup: enter lot size, inspection level, and AQL tolerance, and the calculator returns the sample size and accept/reject numbers. They produce the same result as manual table lookup — they are not a separate standard, just a convenience interface for ISO 2859-1.
For phone trade, the practical inputs are almost always: lot size → Level II → Critical 1.0 / Major 2.5 / Minor 4.0. Committing those to memory is more useful than relying on a calculator for routine orders.
Key Terms
AQL — Acceptable Quality Level. The defect percentage threshold, not a quality score.
Ac (Accept number) — Maximum number of defects in the sample that still allows the lot to pass.
Re (Reject number) — Minimum number of defects that triggers lot rejection. Always Ac + 1.
Lot — The full shipment quantity being inspected.
Sample — The randomly selected subset of the lot that is physically inspected.
ISO 2859-1 — The international standard defining AQL sampling procedures by attributes.