Rainfall is measured in mm not mL

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Rainfall is measured in mm not mL

14/03/2017 7:58am

> From the WeatherWatch archives

With all the rainfall figures coming in from the recent floods a theme was noticed – many of you measure rainfall in millilitres not millimetres.

We thought we’d go straight to the experts to get an explanation. Who better than former MetService Weather Ambassador Bob McDavitt.

Bob says rain is measured in a rain gauge its depth is measured in millimetres (mm).

“A mm of rain spread out over a square metre weighs around 1Kg and takes up 1 litre in volume. if we spread the same depth of rain over a hectare (100m x 100m) then it weighs a tonne / 1000kg”

So 1 mm of rain = 1L per square M.

“Millilitres of rain is probably what hydrologists and roof builders work with” says Bob. “If you know the square metres of your roof (when reduced to a flat surface) then multiply that by the mm of rain to get the litres going into your rain storage tank, so if your place got 50mm of rain last night (two inches) and your (flattened) roof is 50 sq metres then that is 50 x 50 = 2,500 litres into the storage tank, or a quarter of a 10,000 litre tank”.

As to how some people switched from mm to ml? Bob has his theory: “I think that’s happened because the slang term for millimetres of rain is mils of rain, and it is so easy to from mils to ml.”

The correct measurement for rainfall is in millimetres (mm).

– WeatherWatch.co.nz

Comments

Before you add a new comment, take note this story was published on 14 Mar 2017.

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William Llewellyn on 21/05/2024 5:20am

This was written in 2017. We went metric in 1976, so how come 41 years later you are including inches (in brackets) ?
Them that refused to use metric have long since died or moved to America, so it is about time we just used metric, there is no piont including the imperial equivalent … seriously, measurements based on an English king’s body parts has not place in our modern world.
Also, wow, who didn’t pick up the fact that 100 times 100 is not 1,000 ???

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Mike on 29/10/2024 12:23am

Do you spend your life complaining about things that just do not matter?
Very useful article and all you can do is complain about the small things. Get over it

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Ivan on 27/01/2023 7:16am

100×100 = 10000, so its not a ton, but 10 tons.

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Abner Alquiroz Villacorta on 31/07/2024 11:51pm

its maybe he means 1 ton to 1 hectare (w/c 10,000 square meter of land)…. just saying 🙂

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LjAWgTn on 9/05/2022 4:11pm

Hi Bob McDavitt. My partner and I lived above you in the 9o’s in H Rd, HB. We looked after your mail when you went on the Whitbread RtWR! (a great neighbour and a good guy a man on top of his game is Bob McD)
You won’t remember us, we weren’t there that long, 6-12 months, but then again you might ha, but after your name popping up I wanted to attempt to send you kind regards and best wishes for the future. from Lisa

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andy2000 on 4/11/2019 11:11pm

Hiya, I too wonder if you could correct the rate per hectare…it should read 10,000L per hectare.
Cheers.

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rajib nazark on 17/09/2020 9:17am

MY/SG detected in NZ

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Scott on 29/09/2019 6:02pm

Conical, glass full scale marked one liter. At the bottom marked off in mL.

I was looking for a chart to aid in converting this to inches so we could use this old gauge.

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WW Forecast Team on 29/09/2019 6:55pm