Rainfall in Patna
Patna gets 84% of its rain from the monsoon, June to September, and July is its wettest month. In 2025 it got 1,076 mm, 8% above average (normal).
Month-wise rainfall in Patna
Average rain in each month, 2006–2025.
| Month | Average rain | Share of the year |
|---|---|---|
| January | 8 mm | 1% |
| February | 12 mm | 1% |
| March | 10 mm | 1% |
| April | 14 mm | 1% |
| May | 57 mm | 6% |
| June | 142 mm | 14% |
| July | 262 mm | 26% |
| August | 242 mm | 24% |
| September | 187 mm | 19% |
| October | 56 mm | 6% |
| November | 1 mm | 0% |
| December | 3 mm | 0% |
Yearly rainfall in Patna since 2006
Lighter bars are dry years, 20% or more below average (2009, 2010, 2018, 2022, 2024), when wells and borewells are drawn hardest. The last ten years averaged 11% less rain than the ten before.
What Patna's rain is worth to a building
Every millimetre of rain on a square metre of roof is a litre of water. A 100 m² roof in Patna sheds about 84,490 litres in an average year, most of it in four monsoon months. Sent into a recharge pit, it refills the ground instead of flooding the street.
Your building: how much can you recharge?
1 mm of rain on 1 m² is 1 litre. The surface factor allows for water lost to splash, evaporation and first-flush.
Frequently asked questions
What is the average annual rainfall in Patna?
About 994 mm a year, averaged over 2006–2025 from NASA POWER satellite and weather-model data for the centre of the district. The wettest year in that time was 2008 (1,576 mm) and the driest was 2018 (614 mm).
Which month gets the most rain in Patna?
July, with 262 mm in an average year, followed by August and September. November is the driest month (1 mm).
How much of Patna's rain falls in the monsoon?
84% of a normal year's rain falls from June to September. 6 months average 50 mm or more.
How much did it rain in Patna in 2025?
1,076 mm, which is 8% above the 2006–2025 average, or "normal" in the India Meteorological Department's terms.
Is rainfall in Patna increasing or decreasing?
The last 10 years averaged 11% less rain than the 10 before them. Year-to-year swings are still bigger than that change.
How much rainwater can a house in Patna harvest?
A 100 m² (about 1,076 sq ft) concrete roof in Patna sheds about 84,490 litres in an average year: area × rainfall × 0.85 for splash and evaporation. Sent into a recharge pit, that refills the ground under the house instead of running into the drain.
Rainfall from NASA POWER (bias-corrected satellite and weather-model rainfall) at the centre of Patna district. It reads close to, but not exactly the same as, India Meteorological Department rain-gauge totals, and rain varies within a district.