The standard unit of measuring agricultural land is Hectare, Bigha, and Guinea.

Explanation:
1. Hectare:
- A hectare is a unit of measurement commonly used in agriculture to measure large areas of land.
- It is equal to 10,000 square meters or 2.471 acres.
- Hectares are widely used across the world as a standard unit for measuring agricultural land.
- It provides a convenient and standardized way to quantify the size of land for various purposes, such as buying, selling, or leasing agricultural land.

2. Bigha:
- Bigha is a traditional unit of measurement used in South Asia, particularly in countries like India, Nepal, and Bangladesh.
- The size of a bigha can vary from region to region, as it is not a standardized unit like the hectare.
- In some regions, a bigha may be equal to 1/3 acre, while in other regions, it may be equal to 5/8 acre or even 1 acre.
- Due to the lack of uniformity in its measurement, the use of bigha is not as prevalent as hectares in modern agricultural practices.

3. Guinea:
- Guinea is another unit of measurement used in some parts of India, particularly in the state of Uttar Pradesh.
- It is a smaller unit compared to hectares and bighas.
- 1 guinea is equal to 121 square yards or approximately 101.17 square meters.
- Guinea is primarily used in the context of small landholdings and is not as widely recognized or used as hectares or bighas.

Conclusion:
In conclusion, the standard unit of measuring agricultural land can vary depending on the region and country. However, the most commonly used units are hectares, bighas, and guineas. Hectares are widely recognized and used across the world as a standardized unit, while bighas and guineas are more region-specific. It is important to be aware of the specific unit being used in a particular region when dealing with agricultural land measurements.