The minimum buffer stock norms for the Food Corporation of India (FCI) is 24.3 million tonnes. This buffer stock is maintained to ensure food security in the country and to meet any unforeseen circumstances such as natural disasters or supply disruptions.

Importance of Buffer Stock:
- Ensuring Food Security: Buffer stock helps in ensuring food security by maintaining sufficient quantity of food grains in case of any shortage or emergencies.
- Price Stabilization: Buffer stock helps in stabilizing the prices of essential commodities by regulating the demand and supply in the market.
- Meeting Emergencies: Buffer stock acts as a reserve in case of any emergencies like droughts, floods, or other natural disasters, ensuring that there is enough stock available to meet the immediate needs of the affected regions.
- Distribution during Calamities: Buffer stock also helps in distributing food grains during times of calamities or emergencies when the normal distribution channels might be disrupted.

Factors determining the Buffer Stock Norms:
- Population: The buffer stock norms are determined based on the population of the country and the expected food grain requirements.
- Consumption Patterns: The consumption patterns of different regions and states also play a role in determining the buffer stock norms as it helps in estimating the demand for food grains in different parts of the country.
- Production and Procurement: The buffer stock norms are also influenced by the production and procurement of food grains. If the production is expected to be lower than the demand, higher buffer stock norms may be set to ensure sufficient availability.
- Storage and Handling Capacity: The storage and handling capacity of the FCI and other agencies involved in food grain storage also play a role in determining the buffer stock norms. Adequate storage facilities need to be available to maintain the buffer stock.

Conclusion:
The minimum buffer stock norms for the FCI is 24.3 million tonnes, which is determined based on factors like population, consumption patterns, production and procurement, and storage capacity. This buffer stock ensures food security, price stabilization, and helps in meeting emergencies and distribution during calamities.