Foundation Calculator
Calculate strip and slab foundation: concrete volume, rebar weight, formwork. Online calculator with formulas for house and bathhouse construction.
Total length of all sides, m
Concrete strip thickness, m
Strip height or slab thickness, m
Standard reinforcement bar
Total bars in top + bottom layers
Calculation formula
V = P × b × h L = P × n × 2 W = L × ρ(d)
P — perimeter, b — strip width, h — height. For a slab V = a × b × h. Rebar length is multiplied by linear mass: 8 mm — 0.395 kg/m, 10 mm — 0.617 kg/m, 12 mm — 0.888 kg/m, 14 mm — 1.21 kg/m, 16 mm — 1.58 kg/m.
About the foundation calculator
The foundation calculator helps you quickly estimate concrete volume and rebar quantity for a strip or monolithic slab footing. Just enter the dimensions — the formulas compute cubage and steel weight for you.
For a strip foundation you need the perimeter (total length of all walls), strip width and height. For a slab — length, width and thickness. The tool supports all standard rebar diameters from 8 to 16 mm.
All calculations run locally in your browser — data never leaves your device. The result is suitable for a preliminary estimate for a house, bathhouse, garage or fence.
Advantages
Two foundation types
Strip and slab in a single calculator
Rebar calculation
Length and weight by real linear mass per diameter
Instant result
Volume, length and weight are computed right in the browser
Frequently asked questions
How do I calculate concrete volume for a strip foundation?
Multiply the strip perimeter, width and height: V = P × b × h. For example, perimeter 36 m × 0.4 m × 1.5 m = 21.6 m³ of concrete.
Which foundation should I choose — strip or slab?
A strip is cheaper and suits stable soils and lightweight buildings. A slab is more reliable on heaving soils and under heavy houses, but it needs 1.5–2× more concrete.
Which rebar diameter should I use?
For a residential strip foundation, 12 mm bars are used as main reinforcement and 8 mm for stirrups. A monolithic slab usually takes 12–14 mm in both layers.
How many rebar rows does a strip footing need?
A minimum of 4 bars — 2 in the top layer and 2 in the bottom. If the strip is taller than 80 cm, add a middle row (6 bars total).
Which concrete grade should I order?
For a residential foundation, M250–M300 (C20/25) is used; for a bathhouse or garage M200 is enough. Higher grade means a stronger base.
Do I need to add a concrete reserve?
Add 5–10% on top of the calculated volume for pouring losses, uneven trench bottom and formwork gaps. It is better to have leftovers than to run out mid-pour.