How much color do you need for a 3D image?

How much color you need is mainly determined by the size of the image. But the surface of the ground is also crucial. If it’s old washed-out asphalt, then it’s easy to double the paint. The floor then absorbs a lot of paint.

For regular sidewalk slabs that don’t take much paint, I estimate always half the area indicated on the paint bucket. Roughly estimated, this is quickly 50-80 liters in total for a 300m² picture.
A road with very old asphalt sucks like a sponge. Often I then no longer paint opaque, i.e. over the entire surface, as if spread with a paint roller. The trick is to use a witches’ broom or a tassel to spray the paint on the floor.
In the photo, it still looks as if the entire surface is painted opaquely with the paint.

If I use chalk, then you don’t get very far with quantities. For the large areas I use pigments, i.e. color powders. This is much faster than using a chalk pen.

Chalk paintings are maximum 100m² and pigments you need roughly 5-10kg. What amount of chalk is then added is up to the chalk and the ground. If the chalk is very soft and crumbly, you can imagine that it runs out faster. If the floor is very rough, the same applies. But 50-100 chalk pens are neccessary or sure.