About

A strip foundation (or continuous footing) is one of the most common structural bases for load-bearing walls. However, estimating materials for it is often fraught with errors due to the linear nature of the calculation versus the 3D reality of corners and intersections. An underestimation leads to halting a pour mid-way—a structural disaster—while overestimation wastes budget on materials that cannot be returned.

This calculator solves the complexity of material takeoffs by computing not just the concrete volume, but also the specific rebar requirements (longitudinal and transverse) and the surface area for formwork. Crucially, it accounts for the total perimeter length and cross-sectional dimensions to provide a precise bill of quantities. Whether you are pouring a simple garage footing or a complex house perimeter, accurate material planning ensures structural integrity and financial control.

Formulas

The core calculation determines the volume of the strip by multiplying the total perimeter length by the cross-sectional area.

V = L × W × D

Where L is total length, W is width, and D is depth. To calculate the formwork area (boards needed for the sides), we use:

A_form = 2 × L × D

Total rebar weight is derived from the number of bars and the specific weight of the chosen diameter:

W_steel = (L × N_bars) × UnitWeight

Reference Data

Concrete Grade	Strength (MPa)	Typical Use Case	Cement (kg/m³)	Density (kg/m³)
M100 (C7.5)	7.5 MPa	Bedding courses, non-structural	160 - 200	2300
M150 (C12.5)	12.5 MPa	Light strip footings, floors	220 - 250	2350
M200 (C15)	15 MPa	Residential foundations, slabs	260 - 300	2380
M250 (C20)	20 MPa	Standard foundations, beams	300 - 340	2400
M300 (C25)	25 MPa	Heavy load foundations, walls	340 - 380	2420
M350 (C30)	30 MPa	Multi-story structures, columns	380 - 420	2450
M400 (C35)	35 MPa	High-rise foundations, aquatic	420 - 460	2480
M450 (C40)	40 MPa	Bridges, heavy infrastructure	460 - 500	2500
Rebar φ8mm	-	Stirrups / Transverse	0.395 kg/m	-
Rebar φ12mm	-	Light Longitudinal	0.888 kg/m	-
Rebar φ16mm	-	Standard Longitudinal	1.580 kg/m	-

Frequently Asked Questions

Professional estimates typically add a safety margin of 5% to 10% to account for spillage, uneven trench excavation, and formwork deflection. This tool calculates the 'geometric volume' exactly. We recommend you order 10% extra to prevent running short during the pour.

The depth of a strip foundation is dictated by the soil type and the frost line in your region. The bottom of the foundation must generally sit below the frost line to prevent frost heave, which can crack the concrete. Consult local building codes or a structural engineer for the specific depth requirement in your area.

M200 (approx. C15) is suitable for light residential structures like sheds or single-story timber houses. M300 (approx. C25) is the standard for substantial residential foundations, capable of supporting two-story brick or concrete block homes. Using a lower grade than required compromises the building's longevity.

Steel reinforcement often represents 25-30% of the foundation's material cost. While concrete is sold by volume, steel is sold by weight. Accurate weight calculation prevents over-purchasing expensive metal and ensures you have enough tonnage for delivery logistics.