Concrete Footing Calculator
Size continuous, spread/pad, and round pier footings — concrete volume (cubic yards, bags, truck loads), rebar quantities, optional crushed-stone base, and a full cost breakdown with a downloadable PDF estimate.
Footing size, depth, and reinforcement must follow your local code and soil/structural design. Quantities are geometric estimates — verify with your engineer or building department. For planning purposes only.
| Bag Size | Yield | Bags Needed | Total Weight | Best For |
|---|
Bag counts cover the full — ft³ (waste included). Bagged mix usually beats ready-mix under ~1 cu yd.
How to use the concrete footing calculator
Four quick steps turn your footing dimensions into concrete volume, rebar, base material, and a full cost estimate — whether you’re pouring a wall footing, column pads, or deck piers.
Pick your footing type
Continuous/strip, spread/pad, or round pier. Each type asks only for the dimensions it needs — or tap a preset like Perimeter 40ft or 6 Deck piers.
Enter dimensions
Width and depth in inches, length or depth in feet, and a count for repeated pads or piers. The tool handles the unit conversions.
Add rebar & base
Set the reinforcement to match your design, toggle a crushed-stone base, and dial in a waste allowance for trench over-dig.
Read results & save a PDF
Get cubic yards, bag counts, rebar linear feet, truck loads, and a full cost breakdown — then download a two-page PDF estimate.
How a footing estimate is calculated
Every footing comes down to volume = area × depth, worked in matching units. Here is the exact geometry behind each footing type, all producing cubic feet.
Worked example — a 40 ft perimeter strip footing (16″ × 8″)
Volume: 40 × (16/12) × (8/12) = 35.6 cu ft
Cubic yards: 35.6 ÷ 27 = 1.32 cu yd
With 10% waste: 39.1 cu ft = 1.45 cu yd (order ~1.5)
Rebar: 3 bars × 40 ft × 1.10 = 132 ft (7 × 20 ft sticks)
Order about 1.5 cu yd ready-mix, plus ~132 ft of rebar.
Footing estimating charts
Handy lookups for common footing jobs, round-pier volumes, typical sizing, and bag yields. Volume figures exclude waste, so add 10% or more for trench over-dig.
| Footing job | Dimensions | Cubic feet | Cubic yards | 80 lb bags |
|---|---|---|---|---|
| House perimeter (strip) | 40 ft × 16″ × 8″ | 35.6 ft³ | 1.32 yd³ | 60 bags |
| Garage wall (strip) | 24 ft × 12″ × 6″ | 12.0 ft³ | 0.44 yd³ | 20 bags |
| 4 column pads | 24×24×12″ × 4 | 16.0 ft³ | 0.59 yd³ | 27 bags |
| 6 deck piers | 16″ dia × 4 ft × 6 | 33.5 ft³ | 1.24 yd³ | 56 bags |
| 8 post holes | 10″ dia × 3 ft × 8 | 13.1 ft³ | 0.49 yd³ | 22 bags |
Under ~1 cubic yard, bagged mix usually beats ready-mix once short-load fees are added. Bag counts exclude waste — add 10%+ for over-dig.
| Diameter | Cu ft per ft | 4 ft pier (cu ft) | 4 ft pier (80 lb bags) |
|---|---|---|---|
| 8 in | 0.35 ft³ | 1.40 ft³ | 3 bags |
| 10 in | 0.55 ft³ | 2.18 ft³ | 4 bags |
| 12 in | 0.79 ft³ | 3.14 ft³ | 6 bags |
| 16 in | 1.40 ft³ | 5.59 ft³ | 10 bags |
| 18 in | 1.77 ft³ | 7.07 ft³ | 12 bags |
| 24 in | 3.14 ft³ | 12.57 ft³ | 21 bags |
Multiply “cu ft per ft” by your pier depth and number of piers. Bag counts are rounded up and exclude waste.
| Element | Common guidance |
|---|---|
| Wall / strip width | ~2× wall width (e.g., 16″ under an 8″ wall) |
| Strip footing depth | Often 8–12″ thick, min per code |
| Deck / porch pier | 12–24″ dia, below the frost line |
| Bottom of footing | Below local frost depth & on firm soil |
| Pad / column size | Sized to load & soil bearing capacity |
Footing size, depth, and reinforcement are structural decisions. These are typical starting points only — follow your local building code and engineer.
| Bag size | Yield | Bags per cu yd | Best for |
|---|---|---|---|
| 40 lb | 0.30 ft³ | 90 bags | Small post holes |
| 60 lb | 0.45 ft³ | 60 bags | Piers & small pads |
| 80 lb | 0.60 ft³ | 45 bags | Most DIY footings |
Bag counts are always rounded up. Yields are typical for standard pre-mix — check your product’s stated yield.
Everything the calculator works out
One set of footing dimensions gives you every number needed to order and price the pour — whether you’re bagging piers or booking a truck for a foundation.
Key figures every footing depends on
Built for any footing job
From a handful of deck piers to a full perimeter foundation, the same calculator scales to the pour.
Setting deck piers, fence posts, or a shed’s pier footings and wants the exact bag count per hole.
- Start from a preset like 6 Deck piers
- Use the round-pier table by diameter
- See when bags beat ready-mix
Pricing perimeter strip footings and column pads, and needs cubic yards plus rebar footage fast.
- Enter local $/cu yd and $/ft rebar
- Batch identical pads by quantity
- Hand the PDF estimate to the client
Scoping a build with strip footings, pads, and piers all in one materials budget.
- Model each footing type separately
- Total the yards for pour-day trucks
- Use cubic meters for metric specs
7 tips for footings that hold
Footings are structural, so the stakes are higher than flatwork — these habits keep your order right and your foundation on solid ground.
Concrete footing calculator FAQ
The volume, sizing, and reinforcement questions people ask most before pouring footings.
It depends on the footing shape, all worked in matching units:
• Strip / continuous: L(ft) × W(in)/12 × D(in)/12
• Pad / spread: L × W × D (all in ft) × count
• Round pier: π × (dia/2, in ft)² × depth(ft) × count
Divide cubic feet by 27 for cubic yards. Example: a 40 ft × 16″ × 8″ wall footing = 40 × 1.33 × 0.67 = 35.6 cu ft = 1.32 cu yd. Footing trenches over-dig, so add 10% or more for overage.
A footing must sit below the local frost line and bear on undisturbed or compacted soil. Frost depth ranges from near zero in warm climates to 48 inches or more in cold ones.
Many residential wall footings are at least 8 to 12 inches thick, but the required depth and thickness are structural — they depend on the load, soil bearing capacity, and your local building code. Always confirm with your building department or engineer.
A common rule of thumb for wall (strip) footings is roughly twice the wall width — for example, a 16-inch footing under an 8-inch foundation wall, projecting evenly on both sides.
Final width is set by the load above and the soil’s bearing capacity: heavier loads or weaker soil need a wider footing to spread the pressure. Pad and pier sizes work the same way. Size to your structural design and local code, not the rule of thumb alone.
Concrete per foot of depth, by tube diameter:
• 8 in: ~0.35 cu ft/ft • 10 in: ~0.55 cu ft/ft
• 12 in: ~0.79 cu ft/ft • 16 in: ~1.40 cu ft/ft
• 18 in: ~1.77 cu ft/ft • 24 in: ~3.14 cu ft/ft
Multiply by depth and the number of piers. Example: six 16″ piers at 4 ft deep = 6 × 5.59 = 33.5 cu ft ≈ 1.24 cubic yards.
Most structural footings do, to tie the footing together and help it span soft spots.
• Strip / continuous: 2 to 4 continuous bars, lapped at corners.
• Pad / spread: a bar mat running both ways, often 6 to 12 inches on center.
• Round pier: a vertical bar cage with ties.
Bar size, spacing, and concrete cover are structural decisions — follow your engineer’s design and local code, not a generic default.
Deck piers and post holes use the round-pier formula. A 12-inch pier at 4 ft deep holds about 3.14 cu ft (roughly six 80-lb bags). Eight 10-inch post holes at 3 ft deep total about 13 cu ft, or around twenty-two 80-lb bags.
Scattered piers and post holes are usually easiest to fill with bagged mix; a continuous run may be worth ready-mix. Always dig below the frost line.
A few inches of compacted crushed stone under a footing gives drainage and a firm, level bearing surface, which helps in wet or uneven soils. A 4-inch base runs roughly $1.50 per square foot.
Some soils and codes require it; others allow the footing to bear directly on undisturbed soil. Check your local code and soil conditions before deciding.
Under about 1 cubic yard, bagged mix usually wins once ready-mix short-load fees are added — good for scattered piers, post holes, and small pads.
Above roughly 1 cubic yard, ready-mix is faster, cheaper, and gives one continuous pour, which suits perimeter strip footings. A cubic yard is about 45 80-lb bags, so the labor of mixing adds up quickly on larger jobs.
Structural & Estimating Notice: Footing size, depth, and reinforcement are structural requirements that must follow your local building code and soil/structural design. This calculator provides geometric volume, rebar, and cost estimates based on user input and standard material densities — it is not a substitute for engineering. Trenches over-dig, so order overage, and always verify footing dimensions and reinforcement with your engineer or building department before ordering. For planning purposes only.