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Rainfall calculator

Below you can find a little program to calculate the amount of rain water (precipitation) that will fall on a certain surface (your roof or premises). The amount is indicated in m3 (=1000 liters, for US/UK units click here). Also you can add the cost of mains or tap water per M3 to evaluate the cost savings per year if this rainwater is collected and used instead of drinking water.

Fill in your area


If you do not know the area, fill in the length and width, you do not need to fill the area then.  The length and width is optional.
length m
width m
Fill the rain fall (see table) mm
Fill the cost of one cube water:
The volume of rainwater you get is m3/year
so you can save per year:


The first rain gauge dates back to India, 2000 years age (400 BC). The Indians designed a measuring instrument for rain to decide how many seeds they had to plant. Nowadays the whole world measures rainfall. The most wettest place in the world is Mount Wai-'ale-'ale in Hawaii. The rainfall there is 11455 mm per year. Cherrapungi in the foothills of the Himalayas once recorded at incredible  26461 mm per year. The most rain in less than an hour was recorded at Holt, Montana USA received 305 mm of rain in only 42 minutes, on the 22nd June 1947. The highest rainfall per year was recorded at 26 461.2 mm (1041.78''), in Cherrapunji, India, 01 AUG 1860 to 31 JUL 1861. 
Find more on http://www.onlineweather.com/v4/data/weatherfacts/rainfall.html.

On islands it generally rains more than on continental lands. It rains less in the middle east. In the tropical forests it rains a lot. It rains the least in The Western Sahara. Generally speaking it rains the most in South America, followed by East Asia, North America, West Asia, Africa and Europe. Here is a small table of yearly precipitation of some countries:

Country Average annual precipitation in mm
Netherlands 778.3
England 1219.8
Germany 699.9
Belgium 847.4
France 866.7
Russia 460.1
United States 735.5
Mexico 751.5
Surinam 2330.8
Brazil 1782.3
Western Sahara 45.4
Bahrain 82.6
Egypt 51.2
Japan 1667.9
Australia 534.5
Bangladesh 2665.4
Source: http://www.tyndall.ac.uk/data/countries/countries.htm

Go with your mouse over the image!!

If your country is not mentioned above, you can find it in http://www.cru.uea.ac.uk/~timm/climate/cty_new/obs.wei.clim.pre.agg
You can find the rainfall in Europe at http://www.uni-koeln.de/math-nat-fak/geomet/meteo/winfos/precieuropa.gif. This gives the rainfall of the last six hours.


For the Dutch, here are some specifications:

January 2,8°C 5,2°C 0,0°C 67 mm 68 hour
February 3,0°C 6,1°C -0,1°C 48 mm 49 hour
March 5,8°C 9,6°C 2,0°C 65 mm 67 hour
April 8,3°C 12,9°C 3,5°C 45 mm 44 hour
May 12,7°C 17,6°C 7,5°C 62 mm 40 hour
June 15,2°C 19,8°C 10,2°C 72 mm 45 hour
July 17,4°C 22,1°C 12,5°C 70 mm 37 hour
Augustus 17,2°C 22,3°C 12,0°C 58 mm 31 hour
September 14,2°C 18,7°C 9,6°C 72 mm 48 hour
October 10,3°C 14,2°C 6,5°C 77 mm 57 hour
November 6,2°C 9,1°C 3,2°C 81 mm 70 hour
December 4,0°C 6,4°C 1,3°C 77 mm 68 hour

The average weather in De Bilt per month over  1971-2000
Source: KNMI

Find more about water recycling at Lenntech Water Recycling.

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