Building and garden calculators
The core math is a volume or an area. A waste margin (offcuts, redo, relief) is added because a site is not a perfect slab.
Concrete or gravel density depends on the mix. Paint coverage depends on the substrate. Enter real dimensions and read the product sheet for coverage and coats.
Most used
- Concrete calculatorThe math starts from a rectangular box: volume in m³, then a waste margin. Mass uses 2,400 kg/m³, a typical normal-weight concrete density, not every mix.
- Gravel calculatorFor a base course, a path, or drainage: volume comes from the box, mass applies 1,600 kg/m³. That is an order of magnitude; delivered crushed stone can be heavier or lighter.
- Mulch calculatorA bed is not formwork: mulch settles in a few weeks. The math gives spread volume, a small margin, then the equivalent in 50 L bags.
- Paint calculatorQuantity is a division: net area times number of coats, divided by spreading rate in square meters per liter. Spreading rate is read on the product sheet and depends on the substrate.
Subcategories
Volumes
Concrete, gravel and mulch: length × width × depth.
Full list
- Concrete calculatorThe math starts from a rectangular box: volume in m³, then a waste margin. Mass uses 2,400 kg/m³, a typical normal-weight concrete density, not every mix.
- Gravel calculatorFor a base course, a path, or drainage: volume comes from the box, mass applies 1,600 kg/m³. That is an order of magnitude; delivered crushed stone can be heavier or lighter.
- Mulch calculatorA bed is not formwork: mulch settles in a few weeks. The math gives spread volume, a small margin, then the equivalent in 50 L bags.
- Paint calculatorQuantity is a division: net area times number of coats, divided by spreading rate in square meters per liter. Spreading rate is read on the product sheet and depends on the substrate.
- Flooring calculatorNet area is the room rectangle. A cutting margin is added (10% default, 25% at most) to match an order in boxes, planks, or tiles.
Questions
Should I always add 10% waste?
No. 10% is a reasonable default for many slabs and floors. Complex layout, an uneven substrate or a pattern needs more. A simple rectangle may need only 5%.