Hi guys,
I'm on holidays without much to do, so I've decided to dig another driveway.
Does anyone know how to calculate the area of my new drive way?
Obligatory MS Paint diagram
I need to work out how much gravel to order.
Thanks so much!
How Do I Calculate Area of New Driveway?
jonagrah on 03/05/2020 - 13:55
Last edited 03/05/2020 - 14:29 by 1 other user
Last edited 03/05/2020 - 14:29 by 1 other user
Comments
depends on how deep you want the gravel to go?
i'd just simplify the area to take off the jagged bit at the top and make a rectangle. approx 9m long x 3m wide. assume 200mm deep of gravel = 9x3x0.2= ~5.5 cubic metresDivide it into a number of triangles (1/2 x h x b) and rectangles (h x b) then sum them.
I was so bored that I used some software to fix your diagram to scale and work out the area to be 25.254 sqm
Thank you so much!!!
I chopped it into two triangles and a rectangle. It was "close enough" to chop the complex shape at the top into a straight line, the small triangle outside the hypotenuse roughly equals the small triangle inside, so they cancel each other. I was able to deduce a number of missing dimensions and angles. The AREA of the lower triangle ~4m² + the middle rectangle 16.5m² + the approximate upper triangle 2m². The TOTAL AREA is 22.5m². Multiply by the depth of gravel you require, round up to the nearest half-cubic meter. That should be the amount of gravel you need to order. Of course, quantities delivered are usually a (pretty good) guesstimate of how much volume a cubic meter is, and may compact more or less than you anticipate. Therefore there is a bit of a margin for error — too little can be spread around a little thin, or too much can be compacted in more or spread wider.
Unfortunately in the diagram you created, the 3m area is wider at the bottom than the top. You are also assuming the sketch angles are accurate, they aren't. The diagram will tend to skew the short side relative to the long side, affecting the positions of the diagonals and in turn affecting the areas within the triangle boundaries. Unfortunately you have no fixed angles/right angles in your sketch, so it is the same as trying to work out the area of a rhombus. It could be very rectangular, or very flat, affecting the calculation significantly. Good try though.
I derived the dimensions below mathematically, after determining the exact position of a right angle in the lower triangle (we know the hypotenuse and one side, so can use the Pythagoras Theorem to calculate the missing side). We can then remove the central rectangular section leaving another triangle at the top (the margin of error in comparing the outlier areas will be less than the margin of error in a front-end-loader scoop of gravel, so I deliberately ignored it). Adding the 3 shapes gave me a mathematically derived area of 22.5m².
Try again using your software, but this time, lock in an angle of 48.59° for the angle at the very bottom of the sketch. I'm sure you will get closer to my answer of 22.5m².
You're right provided that the driveway is exactly 3.0m wide, but the diagram says that was approximate.
That's absolutely right, I would have liked there to be a width measurement at the top and bottom of the block. We know it isn't exactly 3.0m, but we are assuming it is approximately that, and that it is parallel. What is the point of building one that isn't? And 3m wide is a common size and handy goal for a driveway. It was the only measurement I had faith in making assumptions about, due to the lack of angles and only perimeter measurements supplied, it could have been anything. I needed somewhere to start :)
I assume if someone is drawing a sketch, they will be pretty close to representing right angles fairly accurately if they exist. However if we look at the "dog-leg" at the top left, and assume the major overall dimension is 3m, this shape doesn't make sense. 3m wide would make the diagonal measurement at the top 3.3m, yet the two flat measurements of 2.4+1.5m = 3.9m, an overlap of 0.6m. Yet somehow we are meant to insert a 0.7m leg in this 0.6m at get it at right angles? It doesn't fit. We really need a few more accurate measurements and locking down an angle or two.
Adding the 3 shapes gave me a mathematically derived area of 22.5m².
Essentially what whooah1979 derived below… ((9.5+5.5)3/2)1.02
I'm still trying to follow the steps he took in calculating it, it is eerily accurate but makes no sense to me.
EDIT: looks like it's close to using a formula for the area of a trapezoid.
A=((a+b)/2)*h
Zoom in on google earth and use the measurement tool. It's surprisingly accurate and will give the surface area.
((9.5+5.5)3/2)1.02
A+
I don’t know the answer, but I also don’t think you should ask people on the internet. Just in case you get someone like my husband who answers.
He and his father were once working out how much turf we would need for our 600m2 block. He and his dad were adamant it was 650m2 even though this was a bigger size than the block and there was a house on it. I tried to tell them this only to get a very long winded explanation about the footpath etc. I just nodded and pretended I agreed. Rang the supplier and revised our order down to 300m2. We were slightly short but at least we didn’t wasted money on 350m2 that wasn’t needed.
just divide it onto little triangles and squares
Are you going to compact it properly? That will increase the amount of material needed.
Using maths
Surely an adult would be able to calculate this themselves?
Maybe some have not got the skill set others have.
In any case it nice to help out fellow OzBargainers.
Length(m) x Width(m) x Depth(m) = cubic metres(m3) of gravel