The Open-Source Garment Industry Toolkit — Eight Free Calculators on npm and PyPI

S
Santosh Rijal
· May 11, 2026 · 9 min read Garment Industry

Over the last two years building Scan ERP for our own CMT factory in Nepal, I kept writing the same garment-industry formulas in different places — SMV calculation, AQL sample sizing, DHU benchmarks, line efficiency, fabric consumption, CMT cost. Then I would lose them. Then I would write them again.

So I published them. Eight production-tested, MIT-licensed packages on npm (for Node.js / TypeScript) and PyPI (for Python) — the exact same code we use in production every day. No accounts, no email signup, no paywall. npm install or pip install and you have the formula.

Why these formulas needed packages

Most garment-industry quality and costing formulas live in spreadsheets, PDF reference books, or articles on OnlineClothingStudy and Fibre2Fashion. They are accurate, but if you are a developer building software for a factory — an Industrial Engineer dashboard, a costing tool, a quality-control app — you have to read the article, transcribe the formula into code, decide your own validation rules, and hope you got the edge cases right.

I got them wrong more than once. For example, the AQL sampling table from ISO 2859-1:1999 Table II-A has a specific column-offset pattern where the accept/reject numbers slide diagonally as inspection level changes — transcribing it from a PDF is fragile. We caught and fixed a column-offset bug after cross-verifying against published QIMA reference values. Tests caught it. Without tests, that bug would have been silently rejecting good shipments or accepting bad ones.

The eight packages

1. SMV / SAM Calculator

What it does: Stopwatch-method SMV calculation with PA (performance rating) and allowance percentages. Returns basic time, normal time, and standard time.

Why it matters: SMV (Standard Minute Value) is the foundation of every other metric — piece-rate, line efficiency, CMT cost, capacity planning. If your SMV is wrong, everything downstream is wrong.

2. Piece-Rate Calculator

What it does: Calculates operator earnings from piece-rate, with optional quality bonus (15% for 90+ score with no defects), speed bonus (10% for 10%+ faster than target), and overtime (1.5× after 8 hours).

Why it matters: Piece-rate is how most operators in garment factories are paid. Disputes over earnings are the #1 source of factory floor unrest. A single source of truth eliminates "the supervisor calculated it wrong" arguments.

3. AQL Sampling Calculator (NEW)

What it does: Implements ISO 2859-1:1999 Table II-A — given lot size, inspection level (GI/GII/GIII) and AQL level, returns sample size, accept/reject numbers, and an accept/reject decision function. Includes 3-tier garment inspection (critical AQL 0.65 + major AQL 2.5 + minor AQL 4.0).

Why it matters: Every shipment to a brand buyer is inspected against AQL. If you sample wrong, you either ship defective product or reject good lots. Cross-verified against QIMA's published reference (L+AQL2.5 = Accept 10, Reject 11).

4. DHU Calculator (NEW)

What it does: Calculates Defects Per Hundred Units — the standard daily QC metric. Supports breakdown by defect type (broken-stitch, sizing, color-shade), aggregation across multiple checkers, and classification against industry benchmarks (EXCELLENT ≤5%, GOOD ≤10%, ACCEPTABLE ≤15%, POOR ≤25%, CRITICAL >25%).

Why it matters: Read more in our deep dive on how we cut rejection from 8% to under 3%. DHU is the leading indicator — rejection rate is the trailing one.

5. Line Efficiency Calculator (NEW)

What it does: Efficiency % = (Output × SAM) / (Workers × Hours × 60) × 100. Also computes target output for a desired efficiency, required worker count for a target, and line-balance / bottleneck analysis from per-operation SAM data.

Why it matters: Bangladesh/India/Nepal industry average is ~50%. World-class is 75%+. Every percentage point of efficiency improvement reduces your CMT cost directly. Knowing the bottleneck is the first step.

6. Fabric Consumption Calculator (NEW)

What it does: Knit method (GSM × area for T-shirts, polos, hoodies) and woven method (marker length / pieces per marker for shirts and trousers). Adds wastage allowance, converts between GSM and oz/yd².

Why it matters: Fabric is 60-70% of garment cost. Quoting CMT without accurate fabric consumption is how factories lose money on contracts.

7. CMT Cost Calculator (NEW)

What it does: Per-garment CMT cost = (SAM × CPM / Efficiency) + Trims + Packaging. Calculates CPM from your factory's monthly cost. Compares CMT across countries using built-in CPM defaults (Bangladesh $0.10, India $0.18, Vietnam $0.16, USA $1.00, etc.).

Why it matters: When a brand asks "why is your quote $4.20 when Bangladesh is $3.50?", you need to be able to defend each input — not just the bottom line.

8. Bundle ID Generator

What it does: Generates and parses garment-industry bundle QR codes in the format STYLE-LOT-COLOR-SIZE-BUNDLE#-COMPONENT. Includes validation.

Five-minute quickstart

Node.js

npm install garment-aql-calculator garment-dhu-calculator garment-line-efficiency garment-fabric-consumption garment-cmt-cost

// Quote a T-shirt from Nepal at 50% line efficiency
const { calculateCMTCost } = require('garment-cmt-cost');
const { calculateKnitConsumption } = require('garment-fabric-consumption');

const fabric = calculateKnitConsumption({
  bodyLength: 70, chest: 56, sleeveLength: 22, sleeveWidth: 22,
  gsm: 180, wastagePercent: 8,
});
// → per garment 0.190 kg, per dozen 2.28 kg

const cmt = calculateCMTCost({ sam: 15, cpm: 0.09, efficiency: 0.5, trims: 0.30, packaging: 0.20 });
// → CMT $3.20 per garment

Python

pip install garment-aql-calculator garment-dhu-calculator garment-line-efficiency garment-fabric-consumption garment-cmt-cost

from garment_aql_calculator import calculate_aql

# QC sampling for a 2,400-piece shipment
plan = calculate_aql(lot_size=2400, inspection_level="GII", aql=2.5)
# → sample 125 garments, accept ≤7 defects, reject ≥8
print(plan["sample_size"], plan["accept_number"], plan["reject_number"])

What's tested, what's not

Every package ships with an inline test suite that cross-verifies against published industry references — QIMA's AQL examples, OnlineClothingStudy's DHU worked examples, hand-checked GSM-area calculations. As of release, 327 tests pass across the five new calculators (npm + PyPI combined).

What is not tested: country-specific labour cost defaults will go stale as wages rise. They are intentionally exposed as a constant (COUNTRY_CPM_DEFAULTS) so you can override per-factory rather than relying on the bundled value.

Why we open-sourced this

Three reasons.

First: the formulas are not proprietary. ISO 2859-1, DHU, line-efficiency, fabric GSM — these are public knowledge that hundreds of factories already use. The only value-add of keeping them internal would be artificial scarcity.

Second: our actual product is the integrated ERP, not the calculators. Scan ERP connects the SMV to the work pool to the operator earnings to the QC dashboard to the Pi-attached label printer. Anyone can use these calculators standalone; the integrated workflow is what factories pay for.

Third: if a junior IE in a Bangladesh or Vietnam factory uses these to build a tool that helps their plant, that is a good outcome regardless of whether they ever become a Scan ERP customer.

Roadmap

Likely additions over 2026, ordered by how often we use them internally:

Issue requests and PRs are welcome on the individual GitHub repos.

Related reading

About: Santosh Rijal is a medical doctor and the founder of Scan ERP, a manufacturing ERP for CMT garment factories. He owns and operates a knit garment factory in Nepal. Connect on GitHub.