Can anyone do this sum because I have given up

[TheMustressMhor]

Okay - so we are putting concrete slabs on a small area of the garden.

This measures 12 ft x 8 ft.

The slabs we have chosen measure 450mm x 450 mm.

My brain has fallen out trying to work out how many slabs we will need.

Even the woman in the shop got three different answers and eventually sold us 36 slabs.

I think 36 slabs is wrong.

But the fact that I am incapable of working this out is driving me mad. My brain has fallen out and I appeal to anyone who has any sense to tell me how many slabs we need.

TIA

TheMistressMhor - I am also in a small village in Argyll ...

For future reference, I do think that the safest (and cheapest) method is to assume;

a) Shops will usually try to sell you far too many.
b) People fall over themselves when they try to use Mathematics to solve real problems.
c) Perfectly capable people start dropping and breaking things like never before when they start cutting bits to fit.

The most reliable reckoning is using pictures. Draw a scale version of the space (preferably on squared paper), making sure that you have a good centre point that is on a line. Then draw in each square individually with no spaces between them (to allow for somebody forgetting to leave gaps between them glares at builders who forgot when building mine ). Then neatly draw each full square (or rectangle) to fill in the space. Count the number (write 1, 2, 3, 4 on the diagram) to fill the space. Then start looking at the size of the gaps and, depending upon the average competence of the person who is laying them, start writing in numbers for the smaller bits.

I always think it's better to have full slabs wherever possible and minimise the number of cuts from the start.

This thread makes me feel better about my abysmal maths skills . Good luck!

Probably the poster who queried the size of the slabs got mixed up and thought I meant 45mm x 45 mm.

That really would be small slabs.

I haven't told you, have I, about the time DH ordered secondary double glazing panels in millimetres instead of centimetres. They arrived in a very small padded envelope...

1.47638 x 1.47638 = 2.1796979044 feet squared

(Seeing as people are still talking long after the question has been resolved...) I carry out and check calculations as part of my job. If people write every single number on the calculator down in their calculations it straight away makes me dubious that they know what they're doing. (Not trying to pick on you Gingernaut, and I realise it's not exactly critical for paving slabs!)

are they not 4500 x 4500?

Slabs 4 and a half meters squared?? Really?

I think, Tighnabruaich that we are but a ferry ride apart.

DH's mother was born in Tighnabruaich.

whatsthecomingoverthehill

I was always told to round up only at the very end.

Rounding during the calculation adds to any errors.

@CockwOmble

Are the slabs definitely 450mm x 450mm as this seems very small; are they not 4500 x 4500?

That would make it 14ft x 14 ft, as high as a bungalow! They’d only need one but it would have to be winched in place by a massive crane and trimmed by flamethrower to fit in!

OP there is one definite answer and that’s more slabs needed!
And unless people can see the exact area, you can’t say whether you’ll reuse off cuts instead of needing another slab.
Good luck!

I really don't get how people couldn't work this out... Probably the people that say "errrr ill never need this in real life" at school. The woman in the shop is a moron and has no business working there if she can't do such a simple calculation.

Well that's a bit fucking rude

Well come on then 2monstermash - give me the definitive answer.

give me the definitive answer

TheMustressMhor - full disclosure - I'm not actually where my user name would indicate. But not too far away.

Gingernaut, whoever told you that is wrong! The accuracy of the number should reflect the real life tolerance involved. So for paving slabs they're probably not made to tighter than 1mm tolerance.

Order 60 slabs ...return the ones you dont use! I haven;t tried to work it out though just going on the great minds of previous posters who have!!!

64

12x8 = 96
96 ÷ 1.5 = 64

I'm rubbish at maths I asked dh!

Cut out a peice of cardboard the size of the slabs and count how many you will need. Life is too short for that shit 😂

44

1.47638 x 1.47638 = 2.1796979044 feet squared

At the risk of being a pedant it's actually squared feet.

12x8 = 96
96 ÷ 1.5 = 64

No, you're dividing an area, the 96, by a length. If you want to do it this way it should be 96/(1.5x 1.5), area/area 96/2.25 = 42,66666.... .

However, there can't be a 'right' answer to this problem as the context needs to be considered, cutting slabs, spacing etc., that's why there are so many answers.

@mrsBtheparker - I fear you took too much risk being a pedant. The unit that measures 1 foot by 1 foot is a square foot not squared foot.

I think "feet squared" is clearly the same thing as a square foot, although if you talk about a 10 foot square space, that implies 10 feet by 10 feet which is a 100 square foot or square feet space.

Yes, consider myself the victim of Friday evening, it is indeed square feet.
However feet squared and square feet are different.

6 feet squared is 6x6 = 36 square feet.

6 square feet can by anything that results in 6, 1x6, 2x3, 4x1/12 etc, an infinite number of possibilities.

Its pretty easy. 450mm is 18" or 1.5'

Your space is 12' x 8'

So you need
8'/1.5 = 5.3 so 6 whole tiles
12'/1.5 = 8 tiles

= 6x8 = 48 tiles.

Or said a different way, you need 6 rows of 8 tiles to cover the space.

Personally, I'd be inclined not to cut and try to keep it to full tiles - you'd only lose 6" on the width (8' side). That would mean you need 40 tiles. If you want slate chip around the edge, that would probably work.