Earthworks

If I remember correctly (please correct me if I'm wrong) the specific weight of dry sand is 1.8 t / m³.

150t / 1.8 -> 83 m³.

I would consider that "too little" now. If in doubt, just ask the offer creator how many m³ the 150 tons are.

Your house will be built how? With a basement on a slab? Should only the house be slightly elevated, or also the surroundings? If it's just the house, and the house is about 10x10 m, then that is directly under the house 50 m³. But it has to be a bit more. Are the 50 cm also including what has to be removed as topsoil and the slab taken into account?

I think the factor 1.8 won't quite be enough for sand... our sand-gravel-grit mixture has this factor. If you want to be sure, calculate with a factor of 2.

That would be 75 m³ or 150 t in the upper case.

But the price difference is not that big. We pay almost €10,000 for delivery, compaction, and plate load test for 320 m³ of gravel, so almost 600 tons. That is about €17 per ton, including labor. For 50 tons difference, that's just under €900.

Our house will be 15.20 x 9.80 in size. We are building a bungalow without a basement. We have now decided on a different offer; 300 m³ will be delivered there. That should fit much better. Thank you for your answers!

Are you sure? 300 m³ ... that means you want to pile up 600 m² with half a meter?

Yes, that is planned... Actually even 700 m².

How does such a change suddenly come about... I mean, that is almost 4 times as much as in the original post. Did the first provider miscalculate that badly? Or is it simply being built differently now?

We also need 320 m³, so 600 tons, and therefore I know how much that is. We fill 300 sqm by one meter. That is enough for the house, the garage, the driveway and the terrace.