What does UOM mean on an invoice?

On an invoice, UOM is the unit that the quantity column is measured in: 10 PCS means ten pieces, 2 KGS means two kilograms. Under rule 46 of the CGST Rules, 2017, a GST tax invoice shows the quantity of goods with its unit or Unique Quantity Code (UQC), so the buyer and the tax system read the quantity the same way.

What is UOM conversion, and how does it work for cartons and pieces?

UOM conversion turns a quantity in one unit into another using a fixed factor. If a carton holds 24 pieces, receiving 10 cartons adds 10 × 24 = 240 pieces to stock, and an order for a pack of 2 takes 2 pieces. Set the factor on the item record before the first delivery, and check it against the supplier's packing.

What is the difference between base UOM, purchase UOM and sales UOM?

The base UOM is the smallest unit you track stock in, usually the piece. The purchase UOM is how the supplier sells to you, such as a carton of 24. The sales UOM is how the customer buys, such as a single piece or a pack of 2. Stock is always kept in the base UOM and converted from the others.

What is UQC in GST, and how is it different from UOM?

UQC stands for Unique Quantity Code, the expansion used in the CGST Rules; some guides write "unit quantity code". It is a standard unit code used on GST documents, such as NOS, PCS, KGS or BOX. UOM is the general idea of a unit, and a business can name its units however it likes in its own system. E-way bills take the unit from the standard code list, and a GST invoice shows the unit or its UQC.

What does "NOS" mean as a unit on an invoice?

NOS means numbers. It is the unit code for items counted by number, listed as "NOS NUMBERS" in the e-way bill system's master list of units. It sits alongside PCS for pieces, PRS for pairs and SET for sets. Use the code that matches how the item is actually sold and counted, and use it the same way every time.

What problems does a wrong UOM cause in a warehouse?

A wrong UOM makes stock figures wrong by the conversion factor. Receiving 10 cartons as 10 pieces makes 230 units disappear on paper, so the product shows out of stock online. The reverse inflates stock and can lead to overselling. Wrong units also cause pick and pack errors, GRN disputes with suppliers, and invoice quantities that don't match the goods.

What does UOM mean on a supplier's price list or purchase order?

It is the unit the price and quantity refer to. "₹4,320 per CTN, 24 PCS per CTN" means the price is for a carton of 24 pieces, or ₹180 a piece. Check the UOM before comparing prices or placing an order: 10 at ₹4,320 means 10 cartons, or 240 pieces, not 10 pieces.

What is UOM (unit of measure)?

UOM stands for unit of measure: the unit in which an item is counted, bought, stored or sold, such as a piece, pair, kilogram, litre, box or carton. One product can have several UOMs, for example bought in cartons and sold in pieces, so the item record holds a conversion factor between them.

UOM is also used as a short form for some universities. This page is about units in inventory and on invoices.

How UOM works in an Indian D2C or omnichannel warehouse

Three UOMs on one item

Base UOM: the smallest unit you track stock in, usually the piece or the sellable unit. All stock figures are kept in it.
Purchase UOM: the unit the supplier sells in, such as a carton of 24. A supplier’s MOQ may be stated in it.
Sales UOM: the unit the customer buys, such as one piece, or a pack of 2 sold as one listing.

The conversion factor says how many base units are in one purchase or sales unit: 1 carton = 24 pieces; 1 pack of 2 = 2 pieces.

Example: a serum in three units. All numbers are illustrative.

A serum is stocked in pieces (the base UOM), bought in cartons of 24, and sold both singly and as a pack of 2.
Receiving 10 cartons adds 10 × 24 = 240 pieces to stock.
A pack-of-2 order takes 2 pieces from stock; a single takes 1.
If the GRN records “10” in pieces by mistake, the system shows 10 pieces instead of 240. Once a few orders are shipped, the serum shows out of stock online while 230 pieces sit on the shelf.

Common units and their GST unit codes

GST invoices show quantity with a unit or Unique Quantity Code (UQC). These codes are from the e-way bill system’s master list of units:

Unit	Code
Pieces	PCS
Numbers	NOS
Pairs	PRS
Sets	SET
Packs	PAC
Box	BOX
Cartons	CTN
Dozens	DOZ
Kilograms / grammes	KGS / GMS
Litres / millilitres	LTR / MLT
Metres	MTR
Bottles	BTL

Where UOM matters in the warehouse

Receiving: count in the purchase UOM, record in the base UOM.
Storage: bins and labels show the base UOM, and case packs are labelled as cases.
Picking and packing: the pick list shows how many base units make up each order line.
Kitting and packs: a pack of 2 or a gift kit draws its component units from stock.

Common mistakes

A different base UOM per channel, such as pieces on the website and packs on a marketplace, so stock figures can’t be compared.
No conversion for case packs, so cartons are received as pieces.
Decimal quantities for countable items, such as 0.5 of a shirt, usually from a bad conversion.
Changing an item’s base UOM after it has stock, which breaks every past movement.

UOM error rate at receiving = GRN lines corrected for a unit mistake ÷ GRN lines × 100. Example: 3 of 600 = 0.5%.
Conversion check = units received in base UOM ÷ conversion factor. Example: 240 ÷ 24 = 10 cartons, matching the invoice.
Stock in base units = cartons × units per carton + loose units. Example: 7 × 24 + 9 = 177 pieces.

UOM in the Indian context

GST invoices. Rule 46 of the CGST Rules, 2017 says a tax invoice contains the “quantity in case of goods and unit or Unique Quantity Code thereof” (rule 46(i)). The UQC is that standard unit code.
The code list. The e-way bill system’s master list of units includes NOS (numbers), PCS (pieces), PRS (pairs), BOX, CTN (cartons), PAC (packs), KGS (kilograms) and LTR (litres), among others. Use the code that matches how the item is sold.
Packaged goods labels. The Legal Metrology (Packaged Commodities) Rules, 2011 require each retail package to declare “the net quantity, in terms of the standard unit of weight or measure”, or the number of items where the commodity is sold by number (rule 6(1)(c)). Wholesale packages declare the number of retail packages inside or the net quantity (rule 24(c)).

How Fretron CommerceOS fits

Fretron CommerceOS is order, warehouse and shipping software for Indian D2C, retail and omnichannel consumer brands. It is a separate product from Fretron’s freight TMS.

Questions and answers

What is the full form of UOM?: UOM stands for unit of measure. In inventory, purchasing and invoicing, it is the unit in which an item's quantity is counted, bought, stored or sold, such as a piece, pair, kilogram, litre, box or carton. The same item can have different UOMs for buying and selling, linked by a conversion factor such as 1 carton = 24 pieces.
What does UOM mean on an invoice?: On an invoice, UOM is the unit that the quantity column is measured in: 10 PCS means ten pieces, 2 KGS means two kilograms. Under rule 46 of the CGST Rules, 2017, a GST tax invoice shows the quantity of goods with its unit or Unique Quantity Code (UQC), so the buyer and the tax system read the quantity the same way.
What is UOM conversion, and how does it work for cartons and pieces?: UOM conversion turns a quantity in one unit into another using a fixed factor. If a carton holds 24 pieces, receiving 10 cartons adds 10 × 24 = 240 pieces to stock, and an order for a pack of 2 takes 2 pieces. Set the factor on the item record before the first delivery, and check it against the supplier's packing.
What is the difference between base UOM, purchase UOM and sales UOM?: The base UOM is the smallest unit you track stock in, usually the piece. The purchase UOM is how the supplier sells to you, such as a carton of 24. The sales UOM is how the customer buys, such as a single piece or a pack of 2. Stock is always kept in the base UOM and converted from the others.
What is UQC in GST, and how is it different from UOM?: UQC stands for Unique Quantity Code, the expansion used in the CGST Rules; some guides write "unit quantity code". It is a standard unit code used on GST documents, such as NOS, PCS, KGS or BOX. UOM is the general idea of a unit, and a business can name its units however it likes in its own system. E-way bills take the unit from the standard code list, and a GST invoice shows the unit or its UQC.
What does "NOS" mean as a unit on an invoice?: NOS means numbers. It is the unit code for items counted by number, listed as "NOS NUMBERS" in the e-way bill system's master list of units. It sits alongside PCS for pieces, PRS for pairs and SET for sets. Use the code that matches how the item is actually sold and counted, and use it the same way every time.
What problems does a wrong UOM cause in a warehouse?: A wrong UOM makes stock figures wrong by the conversion factor. Receiving 10 cartons as 10 pieces makes 230 units disappear on paper, so the product shows out of stock online. The reverse inflates stock and can lead to overselling. Wrong units also cause pick and pack errors, GRN disputes with suppliers, and invoice quantities that don't match the goods.
What does UOM mean on a supplier's price list or purchase order?: It is the unit the price and quantity refer to. "₹4,320 per CTN, 24 PCS per CTN" means the price is for a carton of 24 pieces, or ₹180 a piece. Check the UOM before comparing prices or placing an order: 10 at ₹4,320 means 10 cartons, or 240 pieces, not 10 pieces.

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Last reviewed: 7 November 2026 by Fretron.

Sources

Central Goods and Services Tax Rules, 2017, rule 46 (CBIC compilation, as amended to 1 June 2021). CBIC. https://cbic-gst.gov.in/pdf/01062021-CGST-Rules-2017-Part-A-Rules.pdf (accessed 5 Nov 2026).
Master codes list (Unit). E-Way Bill System API documentation. https://docs.ewaybillgst.gov.in/apidocs/master-codes-list.html (undated page; accessed 5 Nov 2026).
Legal Metrology (Packaged Commodities) Rules, 2011, with all amendments, rules 6(1)(c) and 24(c). Department of Consumer Affairs. https://consumeraffairs.gov.in/public/upload/admin/cmsfiles/whatsnews/Book_on_Legal_Metrology_Packaged_Commodities_Rules,2011_with_all_amendments_whatsnews.pdf (accessed 5 Nov 2026).