Sodium hydroxide (caustic soda) in flakes or lye, and potassium hydroxide.
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Caustic Soda falls under HSN 2815, in chapter 28 (Inorganic chemicals).
Caustic soda is heading 2815, with flakes in 281511 and lye in 281512. It is taxed at 18%. Soda ash (sodium carbonate) is a different chemical of heading 2836.
| Code | Description |
|---|---|
| 281511 | Sodium hydroxide, solid (flakes, prills) |
| 281512 | Sodium hydroxide in aqueous solution (lye) |
| 281520 | Potassium hydroxide (caustic potash) |
The GST rate on caustic soda is 18%.
| GST rate | Within a state | Between states |
|---|---|---|
| 18% | CGST 9% + SGST 9% | IGST 18% |
Compare other goods on the GST rates list.
The number of digits depends on your aggregate turnover in the previous financial year.
| Turnover last year | Digits | Write |
|---|---|---|
| Up to Rs 5 crore | 4 on B2B invoices, optional on B2C | 2815 |
| Above Rs 5 crore | 6 on every invoice | 281511, 281512, 281520 |
| Export or import | 8 on the shipping bill or bill of entry | From the Customs Tariff, chapter 28 |
Here is how a line for caustic soda looks on a tax invoice within one state: 1 × tonne at Rs 42,000.00 each, taxed at 18%. The figures are an example, not a market price.
| Item | HSN | Qty | Rate (Rs) | Taxable (Rs) | CGST (Rs) | SGST (Rs) | Total (Rs) |
|---|---|---|---|---|---|---|---|
| Caustic Soda | 2815 | 1 × tonne | 42,000.00 | 42,000.00 | 3,780.00 | 3,780.00 | 49,560.00 |
Sold to a buyer in another state, the same line carries IGST of Rs 7,560.00 instead of CGST and SGST. Make the full invoice with the GST invoice format: it fills in the tax split, round off and amount in words.
Chapter 28 (Inorganic chemicals) covers: Acids, alkalis, gases and other inorganic compounds.
Other pages in chapter 28
Products often bought, sold or invoiced together with caustic soda:
Caustic Soda falls under HSN 2815: sodium hydroxide (caustic soda) in flakes or lye, and potassium hydroxide. Common 6 digit codes are 281511 for sodium hydroxide, solid (flakes, prills) and 281512 for sodium hydroxide in aqueous solution (lye).
18%: CGST 9% plus SGST 9% on a sale within a state, or IGST 18% on a sale between states.
If your aggregate turnover in the previous financial year was up to Rs 5 crore, write the 4 digit code 2815 on B2B invoices (optional on B2C invoices). Above Rs 5 crore, write 6 digits, such as 281511, on every invoice. Shipping bills and bills of entry need the full 8 digit code from the Customs Tariff.
Rates checked on 13 October 2026 against the GST rate notifications in force (GST 2.0 from 22 September 2025). Descriptions are in our own words and are a guide, not a ruling: for a disputed or high value item, check the notification or ask your tax adviser.