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Alankar Mishra

April 26, 2025

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Basics of GST

Difference Between UQC and Unit of Measurement (UOM)

In case you have an interest in business, GST compliance, accounting, or anything else, you might have come across two terms that sound similar but are not the same: UQC and UOM. Many people, specifically those working in Tally ERP, TallyPrime, SAP, or GST filings, often mix both of them. This confusion results in compliance issues, invoices being rejected, and inventory levels not syncing.

Let's gain a better understanding of UQC vs UOM, where each is used, and why it matters the most in GST return filings and e-Invoicing.

Overview Table: UQC vs UOM

Feature	UQC (Unit Quantity Code)	UOM (Unit of Measurement)
Full Form	Unit Quantity Code	Unit of Measurement
Used In	GST returns, GSTR-1, e-invoicing	Inventory, Purchase/Sales, Tally entries
Standard	Fixed codes by CBIC	User-defined/custom units
Examples	NOS, KGS, MTR, LTR	Pieces, Kilograms, Boxes, Packs
Data Format	3-letter codes	Full words or abbreviations
Purpose	Legal reporting under GST	Business operations and stock tracking
Editable	No (fixed by law)	Yes (user can create/edit)

What Is UQC (Unit Quantity Code)?

A UQC, or Unit Quantity Code, refers to a universally accepted three-letter abbreviation that indicates the measurement unit employed in reporting supplies in returns like GSTR-1, GSTR-3B, and e-invoicing databases.

Who Defines UQC?

As defined above, UQC is monitored by CBIC (Central Board of Indirect Taxes and Customs) and associated with GST. When invoicing on the GST portal, it is mandatory to use the codes from the official UQC list.

Why Is It Important?

Mandatory in B2B and B2C invoices in e-invoicing.

Used for HSN-wise summary in GSTR-1.

Any mismatch in UQC can cause the rejection of your GST return

Examples of UQC Codes

UQC Code	Meaning
NOS	Numbers (used for countable items)
KGS	Kilograms (weight-based goods)
MTR	Metre (length-based items)
LTR	Litres (liquid measurement)
BOX	Box (packaged goods)
PCS	Pieces (general usage)

What Is UOM (Unit of Measurement)?

Unit of Measurement, or UOM, is the term specific to measuring a unit in inventory, accounting, or ERP software for monitoring stock levels, purchase orders, and sales.

Where Is UOM Used?

Tally ERP 9 / TallyPrime inventory management.

SAP, Oracle, Zoho Books and other ERP software.

Purchase and sales entries.

Stock item creation

Why Is UOM Flexible?

UOMs are user-defined. This means:

You can set "Box of 12", "Dozen", "Piece", "Roll", "Packet", "Set", etc.

No restriction from the government on UOM terminology.

Can be customized based on your business process, packaging, or local terminology.

Examples of UOM in Business

Box of 25 pens.

1 Packet = 500g.

1 Roll = 100 meters.

1 Set = 3 items

Remember, even if your UOM is "Packet", it must be mapped to the correct UQC like "PAC" (for packet) during GST upload.

How Are UQC and UOM Connected?

The UOM you define in your ERP software must be linked or mapped to the correct UQC for GST filings. Otherwise, your invoices may fail validation, especially in e-invoicing and GSTR-1 returns.

Tally Example

UOM: “Bag of 50 kg” → You define it in Tally for business use.

GST Filing: The System maps it to UQC = KGS, total quantity = 50.

Mapping Logic

UOM (Custom)	UQC (Standard)
Packet	PAC
Box	BOX
Roll	ROL
Nos	NOS
Dozen	DZN
Kilograms	KGS

Why This Difference Matters

For GST Compliance

GST portals don’t accept custom UOMs.

They only accept standard UQC codes.

If your UOM is not mapped to the correct UQC, your GST return will fail

For Inventory Control

UOM helps in batch control, stock valuation, unit conversion, etc.

It supports multi-UOM logic (e.g., 1 Box = 12 Pieces).

For E-invoicing

Every B2B invoice requires quantity + UQC.

Wrong UQC = Invoice rejected at IRP (Invoice Registration Portal).

Real-Life Use Case: Retail Pharmacy

Let’s say you run a pharmacy and manage inventory in Tally.

Your UOM in business:

1 Strip = 10 tablets.

1 Box = 10 Strips = 100 tablets
Tally records sales using “Box” and “Strip” as UOM.

But for GST e-invoicing:

You must use UQC = NOS (Numbers).

You need to calculate and report the following: Total Quantity = 100 NOS

GST Filing Errors Due to UQC vs UOM Confusion

Error Type	Reason
JSON upload failure	Wrong UQC used (not in the official list)
Invoice rejection	Custom UOM entered instead of UQC
GSTR-1 error	Unit mismatch between invoice & HSN summary
E-invoice mismatch	The system can’t map custom UOM toa valid UQC

Tally and UQC: How They Handle the Difference

In TallyPrime or Tally ERP 9, here’s how the system handles UQC vs UOM:

You can create your own UOM during stock item creation.

You can map your custom UOM to the correct UQC under F11 > GST Settings > UQC Mapping.

During e-invoice export, Tally automatically converts UOM → UQC for JSON

This ensures smooth filing without manual errors.

Tips to Avoid Mistakes in UQC and UOM

Always refer to the official UQC list while preparing invoices for GST.

Map all UOMs to their respective UQCs before filing the GSTR-1 and e-invoice JSON.

Use standard abbreviations for stock items UOMs to ensure clarity.

Keep separate business UOM (for internal use) and legal UQC (for GST filing).

In Tally, use the UQC Mapping tool to avoid errors in return submission.

Conclusion

While UQC and UOM may sound like synonyms, their purpose and usage are completely different. UQC is a legal, standardised code that ensures consistency and compliance in the GST ecosystem. On the other hand, UOM is a business-friendly unit used to manage inventory, sales, and purchases.

Mixing them up may not only lead to invoice rejection or GST filing errors but can also cause compliance penalties or return notices. Therefore, every business owner, accountant, and Tally user must understand and respect the line between UQC and UOM because, in modern-day compliance, even a unit mismatch can cost you lakhs.

FAQs

Q1. What is the full form of UQC in GST?

Ans: The full form of UQC is Unit Quantity Code. It is a standardized 3-letter code defined by the government to specify the unit of measurement in GST returns, e-invoicing, and other legal documents.

Q2. What does UOM stand for in accounting?

Ans: UOM stands for Unit of Measurement. It refers to the units used in business operations like sales, purchases, and inventory tracking — such as pieces, boxes, kilograms, rolls, etc.

Q3. What is the key difference between UQC and UOM?

Ans: The main difference is that UQC is a legal unit code used in GST filing and e-invoices, while UOM is a user-defined unit used internally by businesses for inventory and billing purposes.

Q4. Why is UQC important for GST filing?

Ans: UQC is mandatory in GSTR-1, GSTR-3B, and e-invoicing. If the correct UQC is not used, the invoice may be rejected by the GST portal or result in filing errors.

Q5. Can I use any custom unit like ‘Carton’ or ‘Pack’ in UQC?

Ans: No. You must select from the pre-approved UQC codes such as BOX (Box), PAC (Packet), KGS (Kilograms), and NOS (Numbers). Custom UOMs must be mapped to these valid UQC codes.

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