Precision statistical sampling for professional auditors. ISA and PCAOB compliant — no signup, no data transmission, no compromises.
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Each method is grounded in ISA 530 and PCAOB AS 2315. Choose based on your testing objective.
Tests whether each item conforms to a control or procedure. Each item is classified as pass or fail. Industry standard for compliance and control testing.
n = RF ÷ Tolerable Error Rate
Measures the monetary or numerical value of items and projects results to the population. Used for substantive substantive testing of account balances.
n = (Z × σ ÷ E)²
Each monetary unit has an equal chance of selection. Particularly effective for detecting overstatements in skewed populations like accounts receivable.
n = Z² ÷ (2 × E²)
AICPA/ISA audit attribute sampling uses reliability factors (RF) for attribute methods and Z-scores for statistical methods:
| Confidence Level | RF (Attribute) | Z-Score (Variables/MAE) | Typical Use |
|---|---|---|---|
| 90% | 2.31 | 1.282 | Preliminary work, lower-risk tests |
| 95% | 3.00 | 1.645 | Standard audit testing — ISA & PCAOB default |
| 99% | 4.61 | 2.33 | High-risk accounts, regulatory requirements |
All calculations are based on published international and US audit standards.
ISA 530 sets the international standard for audit sampling, used by auditors in over 100 countries. Covers both statistical and non-statistical approaches.
Read ISA 530 on IAASB.orgRequired for audits of US public companies (issuers). AS 2315 addresses determining sample sizes and evaluating sample results in public company audits.
Read PCAOB AS 2315Acceptance sampling standards widely used in manufacturing quality control and increasingly referenced in operational and compliance audits globally.
Read ISO 2859 on ISO.orgAU-C 530 is the AICPA standard for audit sampling applicable to non-public (non-issuer) US audits. Closely aligned with ISA 530 with additional practitioner guidance.
Read AU-C 530 on AICPA.orgClear answers to the questions auditors ask most.
Audit sampling means examining less than 100% of a population to form a conclusion about the whole. ISA 530 requires sample sizes to be statistically valid — too small a sample may not provide sufficient evidence, while an unnecessarily large one wastes resources. This calculator determines the mathematically correct minimum sample size based on your risk parameters.
For all common audit tolerances (3-5%), sample sizes are mathematically identical. Both standards use the same AICPA attribute sampling tables with identical RF factors: 2.31 (90% confidence), 3.00 (95% confidence), 4.61 (99% confidence). At 5% tolerable error with 0% expected error and 95% confidence, both produce n = 60 items. The only PCAOB-specific difference is a 60-item minimum floor that only binds when tolerable error exceeds 5% -- at which point the formula alone would produce fewer than 60. Sources: PCAOB AS 2315 paragraphs .03, .23, Table 1 of the Appendix; ISA 530 paragraphs 5-7; AICPA AU-C 530 (identical tables).
ISA 530 is issued by the IAASB and used in over 100 countries — UK, EU, Canada, Australia, Asia. PCAOB AS 2315 applies to US public company audits required by the SEC. The statistical methods are substantially similar. If you're auditing a public US company, use PCAOB. For international or non-issuer US work, ISA 530 is the standard.
Yes — 0% expected error is the standard starting point for compliance testing when controls are new or have operated without known failures. It produces the most conservative (largest) sample size, which is appropriate when you have no prior error data. If you find errors during testing, reassess your conclusion and potentially increase your sample.
Tolerable error is the maximum error rate you will accept without modifying your conclusion. Set based on your assessed risk of material misstatement. Industry benchmarks: 3–5% for most tests, 1–2% for high-risk areas. Your firm's audit methodology should provide specific guidance on the appropriate level for each engagement.
For large populations (over ~5,000 items), the effect is minimal. For smaller populations, ignoring size can produce an unnecessarily large sample. This calculator applies Finite Population Correction (FPC) automatically when the initial sample exceeds 5% of the population.
95% is the default for most audit tests under both ISA 530 and PCAOB AS 2315. 90% for preliminary or lower-risk work. 99% for high-risk accounts or where regulators specifically require it. Higher confidence always means a larger sample.
Attribute (pass/fail) for compliance testing. Variables for substantive testing of account balances where you need to quantify monetary error. MAE / Monetary Unit when each monetary unit should have an equal chance — especially powerful for detecting overstatements in skewed populations like receivables or inventory.
Yes. The underlying statistical methods apply equally to IT audits, operational audits, and compliance reviews. Replace "population" with your total population of controls, transactions, or items under review. The standards referenced (ISA 530, PCAOB AS 2315) are broadly applicable to any systematic sampling exercise.
Nothing. This calculator runs entirely in your browser with JavaScript — no data is ever transmitted to any server. No IP addresses, no cookies, no tracking pixels, no analytics. Your population sizes, error rates, and results remain completely private on your device.
No. This is a calculation tool implementing publicly available formulas from ISA 530, PCAOB AS 2315, and AICPA AU-C 530. It does not constitute audit advice. The auditor remains responsible for applying professional judgement, selecting appropriate parameters, and forming their own conclusions. Always cross-reference with your firm's methodology.