Foundation Calculator

Combined concrete take-off for a complete residential foundation — continuous footing, stem wall and slab-on-grade. Toggle each component on or off; results show per-component and total in cubic yards.

Building footprint

ft
ft
%

Continuous footing

in
Typical 16″ (residential, 2×6 stud wall above).
in
Minimum 8″ per IRC R403.1. Soil type may dictate more.

Stem wall

in
Typical 8″; 6″ for low-load partition walls.
ft
From top of footing to bottom of mudsill.

Slab-on-grade

in
Typical 4″ residential, 6″ for garage.

Calculation results

Total concrete to order

— yd³

Footing concrete

— yd³

Stem wall concrete

— yd³

Slab concrete

— yd³

Foundation perimeter

— ft

Slab area

— ft²

Per-component volumes are with waste applied. Footing uses building perimeter (length runs share corners — no double-counting). Slab uses full footprint (not adjusted for stem wall — typical stem wall sits outside the slab pour).

Informational only. Foundation design depends on soil bearing capacity, frost depth, seismic zone, and structural load. For any new construction, foundation dimensions must come from a licensed engineer or be code-prescriptive per IRC R403. This calculator is for take-off and budgeting from given dimensions, not for design.

Foundation components

A typical residential foundation has three concrete components stacked:

  • Continuous footing at the base — wider than the wall above, distributes load to the soil. Runs around the entire perimeter at frost-line depth.
  • Stem wall on top of the footing — rises from footing to the bottom of the floor framing (the mudsill). Hides the gap between grade and floor; protects framing from moisture.
  • Slab-on-grade — the floor itself, poured inside the stem wall on compacted gravel and vapor barrier.
Vfooting = perimeter × width × depth = 2(L+W) × Wf × Df
Vstem = perimeter × thickness × height = 2(L+W) × Ts × Hs
Vslab = length × width × thickness = L × W × Tslab

Worked example — 40 × 30 ft house, full foundation, 10 % waste

  • Perimeter = 2 × (40 + 30) = 140 ft
  • Footing 16″ × 8″: 140 × (16/12) × (8/12) = 124.4 ft³ = 4.61 yd³
  • Stem 8″ × 2 ft: 140 × (8/12) × 2 = 186.7 ft³ = 6.91 yd³
  • Slab 4″: 40 × 30 × (4/12) = 400 ft³ = 14.81 yd³
  • Subtotal = 26.34 yd³
  • With 10 % waste = 28.97 yd³

Frequently asked questions

How much concrete for a 40×30 foundation?
A full foundation (16″ × 8″ footing + 8″ × 2 ft stem wall + 4″ slab) on a 40 × 30 ft building needs about 26 yd³ raw, or 29 yd³ with 10 % waste. That is roughly 2-3 ready-mix trucks. Slab takes the biggest share (about 15 yd³).
How deep should a foundation footing be?
Below the local frost line. In northern U.S. states 42-48″; in southern states 12-18″. Frost-heave forces are enormous — even a few inches above frost depth can crack a foundation. Your local code authority publishes the official frost depth for your jurisdiction.
Do I need a stem wall on a slab-on-grade foundation?
For a "monolithic" or "thickened-edge" slab no separate stem wall is needed — the slab thickens at the perimeter into an integral footing. For a "T-foundation" or "stepped foundation", the stem wall is a separate pour on top of the footing. Both meet IRC if designed correctly.
How wide should a footing be?
IRC R403.1 prescriptive table: 12″ wide for 1-storey, 15″ for 2-storey, 18″ for 3-storey on standard soil (1,500 psf bearing). For poor soil or heavy loads, the engineer specifies wider. Footings must always be at least as wide as the wall above plus 4″ projection on each side.
Should I include a vapor barrier under the slab?
Yes — code requires a 6-mil polyethylene sheet over compacted gravel before pouring the slab. It prevents ground moisture wicking into the slab and into framing above. Some jurisdictions require 10-mil or specifically labeled vapor retarder; check local.
What is a monolithic slab foundation?
A monolithic (or "thickened-edge") slab is a single pour where the perimeter thickens into a 12-16″ deep edge that acts as the footing. No separate stem wall. Common in slab-on-grade homes in mild climates with shallow frost depth. Cheaper and faster than T-foundation; not suitable where frost depth exceeds 12-18″.
How long does foundation concrete take to cure?
Framing can begin at 7 days (70 % of strength reached). Backfill against stem walls at 7-10 days minimum. Full design strength at 28 days. In cold weather (< 50 °F) curing slows significantly — use blankets or accelerators if pouring below 40 °F.