Calculating volume in metric

[JC Uknz 1Participant @jcuknz1]

Been using metric for years but always fould up when calculating a volume.

Currently have a boiler 50mm diam and 150mm long

25x25x3.142 x150 gives me 2904562.5

Now the bit that trips me …. converting the cubic mm to litres

Is it 1000x1000x1000? That gives me 0.0029045 which seems awefully small. Judging from my one litre milk bottle it could be about a quarter to a third litre

Boiler for Mamod modification accourding to Aussie boiler regs must not be bigger than one litre.

Side note …

I know Manods go well as they are but this is a Mamod Garrett

Your help much appreciared.

[JC Uknz 1Participant @jcuknz1]

[David JuppParticipant @davidjupp51506]

1 ltr = 1000 cc = 10cm x10cm x10cm = 100mm x 100mm x100mm.

Answer should be 0.29 ltr or so.

[clivelParticipant @clivel]

Hi JC,

25x25x3.142 x 150 is 294562.5 mm3 not 2904562.5 somehow an extra zero crept in there.

1 litre=1000000 mm3

so your boiler should be 0.2945625 litres

Clive

[SteamgeekParticipant @steamgeek]

I make the calculation 0.294 litres, you appear to have an extra 0 in your calculation ( after the 9 )

The conversion from cubic mm to litres is 10E-6 ( move the decimal point six places to the left )

[JasonBModerator @jasonb]

If you work on the fact that 1 litre takes up a space 100mm x100mmx100mm you can work it out a s

0.25 x 0.25x 3.142 x 1.5 =0.295lts

or do it as you have in mm then divide by 1,000,000 (100x100x100)

[Gary WoodingParticipant @garywooding25363]

Posted by JC Uknz 1 on 02/01/2014 07:44:32:

Now the bit that trips me …. converting the cubic mm to litres

Is it 1000x1000x1000?

Not quite. You're 1000 times too small – (and you inserted a zero between the 9 and the 4).

1 ltr = 1000cc

1cc = 1000 cubic mm, so 1ltr = 1000 x 1000 cubic mm.

So your boiler = 0.2945625ltrs.

For volume measurement its much easier to work in cm rather than mm. In which case your calculation would be 2.5×2.5×3.142 x15 = 294.5625cc = 0.2945625ltrs.

[John HaineParticipant @johnhaine32865]

Er, that would be 1E-6…

[Ady1Participant @ady1]

1000cc = 1 litre, like a car

So keep things as cubic cm

2.5 *2.5 *3.14= 19.63 cubic cm

*15cm = 294.52 cubic cm, about 0.3 of a litre

simples!

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

When doing any engineering calculation it is always useful to have a general idea of the magnitude of the answer . You can get this from other similar calculations done before , from practical experience , from much cruder preliminary calculations or from a rough practical test .

In case of this boiler :

If it already exists just fill it with water and run water off into measuring jug . Indeed that would probably give a sufficiently good answer .

If boiler exists only on paper the use any of :

Visual comparison of drawn boiler ( or cardboard mockup) with any existing container of known capacity something like same size and shape – kitchen jug , milk carton or beer glass . Visual comparison could easily be accurate to within 10 % and again that may give a sufficient answer directly .

Regards ,

MikeW

[speelwerkParticipant @speelwerk]

1 litre=1 cubic dm, so if you start the caculation with all the dimensions in dm (decimetre) then your answer is in cubic dm which is equal to litres, 25mm=2.5cm=0.25dm. Niko.

Edited By speelwerk on 02/01/2014 10:29:53

[Michael GilliganParticipant @michaelgilligan61133]

JC U,

It'sprobably obvious by now; but I think it worth noting that your original division by (1000x1000x1000) gives the volume in cubic metres … and one cubic metre is roughly the size of those one tonne bags of sand that they crane off the delivery waggon.

Incidentally, for the purposes of boiler volume, I wouldn't worry about expressing litres to the seventh decimal place. [just think what a tiny volume that last place represents]. !!

As MikeW suggests [and you already knew from your Milk bottle] … Domestic containers are very useful for the "sanity check".

MichaelG.

[S.D.L.Participant @s-d-l]

Posted by JC Uknz 1 on 02/01/2014 07:44:32:

Been using metric for years but always fould up when calculating a volume.

Currently have a boiler 50mm diam and 150mm long

25x25x3.142 x150 gives me 2904562.5

Now the bit that trips me …. converting the cubic mm to litres

Is it 1000x1000x1000? That gives me 0.0029045 which seems awefully small. Judging from my one litre milk bottle it could be about a quarter to a third litre

The easy way is to remember 1000 litres = 1 cubic meter = 1 tonne of water =1000kg

This makes sizing tanks very easy

So if working by dimensions work in meters and multiple by a 1000

eg 0.025 x 0.025 x 3.142 * 0.150 = 0.000294562m^3

multiply by 1000 gives 0.294 liters

this saves worrying about no SI units or units that you don't use much.

The easy way is to weigh boiler empty fill then weigh again difference is weight of water 1 litre = 1kg = 1000 grms so if the difference was 294g would be 0.294lts

Steve

[Russ BParticipant @russb]

And the winner of the quickest combined mistake spotting and volume calculations goes to …..

[jason udallParticipant @jasonudall57142]

50 mm * 150 mm…..about a drinks can…300 ml 0.3 l
Btw 200 l ” forty gallon drum”..seems much more than a cubic meter let alone a fifth. .

[jason udallParticipant @jasonudall57142]

Just checked ( my own disbelief)
44 gal imp
55 gal us
210 l
24 ” dia 36″ high…
Funny seem much bigger..but there goes

[Sub MandrelParticipant @submandrel]

It cheers my Imperial sensitivities to see so many 'up to date' metric head advocating the long-deprecated cubic centimetre!

Neil

[JC Uknz 1Participant @jcuknz1]

Thankyou all for rushing to solve my problem .. the thing to remember apart from the obvious decanting and filling up a known container … would work except I have only got as far as cutting the tube and one end …. .. thanks again

Jason that doesn't relate to me as I drink from glass stubbies

The extra zero comes from my fingers inaccuracy and my brain not checking what they had done

I will remember what Steam Geek wrote "The conversion from cubic mm to litres is 10E-6 ( move the decimal point six places to the left )" … the first bit is above me but the bracketted makes sense

[JC Uknz 1Participant @jcuknz1]

Just realised I could seal one end of he tube with gladwrap and do the decanting in to my 300ml jug.

I remember my first use of metrics was at school during WWII in Mech Drwg when I 'thought' the millimeter markings a much easier way of measuring drawings than the imperial on the other side … I guess it relates to I still have ten fingers and ten toes despite my activities of the following years.

I wonder if it was a metrician's plot that the imperial side of theschool ruler was beveled and flopped around whereas the metric side sat flat on the paper

[FalcoParticipant @falco]

The following was given to me as an explanation of how the metric system ties together in the practical world.

It may help anyone not using to it to visualise the connection between length , volume and weight in the metric system.

The weight measurement is correct only if the contents are water.

A little cube box with sides 1 x1 x1cm. will hold 1ml. of water. The water contents, (excluding the weight of the actual box), will weigh 1 gram. (Think sugar lump)

A cube with sides of 10x10x10cm. will hold 1000 ml. (1 litre), and will weigh 1000 grams or 1 kilogram.(kg). (Think milk carton)

A cube with sides of 100x100x100cm, (ie. 1x1x1metre) will hold 1,000,000ml, or 1000 litres and the water contained will weigh 1,000,000 grams, or 1000kg or 1 tonne, (Think of the builders sand bags mentioned by MichaelG )

John

[steveteeParticipant @stevetee]

This is my problem with the metric system, the calculation is easy as all ( well most then) of the units are related to one another . No poundals or degrees f or calories to struggle with. Making sense of the answer is where the problems begin.

I think that any system that uses the same unit to measure the height of a kitchen work top (900mm) as is used to measure the thickness of a piece of paper (0.01mm) is bound to suffer from problems of where does the decimal point lie, how many zero's?. In the case of this boiler it's not 2.9 litres ( half a gallon) or 0.029 litres ( half a teaspoon) so it must be .29 litres., but you do have to jump the decimal point 5, 6 or 7 places to get an answer that makes sense.

I actually rang up the BBC one morning because there was a government minister and a presenter on the news discussing keeping a jerry can of petrol holding 201 litres in your garage( remember the tanker drivers strike). Some idiot had written 20 litres down as 20l , read out on the radio as 201 litres and neither of them realised they were talking about a volume of around 40 gallons, try picking that up.

We used to have a system with measurements like 'An inch and seventeen thirtytwos, plus or minus five thou'. I mean where could that go wrong

Edited By stevetee on 03/01/2014 00:01:43

[speelwerkParticipant @speelwerk]

The person writing 20litres as 20l is doing it correct, the same goes for grams, it is 20g not 20grms. Niko.

Edited By speelwerk on 03/01/2014 00:24:33

[Mark CParticipant @markc]

I think you might find that the correct way should have a space between the numbers and the letter.

Mark

[speelwerkParticipant @speelwerk]

Posted by Mark C on 03/01/2014 00:35:28:

I think you might find that the correct way should have a space between the numbers and the letter.

Mark

I will keep it in mind. Niko.

[MICHAEL WILLIAMSParticipant @michaelwilliams41215]

The correct and most useful way to write down metric quantities is to use the descriptor lettering as the decimal point and prefix this with the decade count lettering .

For instance : 4756 grammes is 4Kg756

Works well with dimensions :

34.5 Metres is 34M5

0.463 Metres is :
0M463
46CM3
463MM0

Note intrinsic use of significant figures . Used properly it avoids the common use of long meaningless decimal values .

MikeW

[Author]

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