Project estimator
Enter Pad and Footing Dimensions
Overall dimensions include the complete footing edge. The calculator uses a continuous perimeter slope from the inner footing depth to the outer footing depth.
Calculation method
Formula Used
The footing is treated as a rectangular perimeter ring with a linear depth change. This approach is more reliable than multiplying a ring area by a simple average depth.
Inner length = Overall length − 2 × footing width
Inner width = Overall width − 2 × footing width
Center volume = Inner length × Inner width × slab thickness
Ring area = Overall area − center area
Footing volume = di × ring area + (do − di) × [(Li + Wi) × b + (8 ÷ 3) × b²]
Order volume = (center + footing + pedestal) × pad count × (1 + overage)
In the footing formula, di is inner depth, do is outer depth, Li and Wi are inner dimensions, and b is footing width.
Workflow
How to Use This Calculator
- Choose Imperial or Metric before entering dimensions.
- Measure the outer edge of the full footing footprint.
- Enter center slab thickness and the perimeter footing width.
- Enter the inner and outer footing depths.
- Add optional pedestal dimensions when one is present.
- Choose a realistic overage percentage for the work.
- Add bag yield, load capacity, and concrete unit price.
- Review the order quantity before contacting your supplier.
Example Data
| Input | Example | Purpose |
|---|---|---|
| Overall pad | 16 ft × 16 ft | Includes the outer footing edge. |
| Center thickness | 6 in | Defines the interior slab volume. |
| Footing geometry | 18 in wide, 12 in to 18 in deep | Defines the sloped perimeter volume. |
| Overage | 7% | Covers normal field variation. |
Planning guide
Understanding Thickened Sloped Footings
A concrete pad supports equipment, posts, walls, or small structures. A thickened footing strengthens the outer perimeter. The sloped section reduces abrupt geometry changes. It can also simplify forming. Accurate volume estimates prevent delays and costly shortages. They also reduce surplus concrete. This calculator separates the center pad, perimeter footing, pedestal, and waste allowance. It then reports practical ordering quantities. Record dimensions in one measurement system. Convert all drawings before entering values. Keep all field notes with the delivery ticket.
Measure the Overall Footprint
Use the outside dimensions of the footing. Measure length and width at the outer edge. Enter the center pad thickness separately. Enter footing width across the perimeter. The calculator subtracts both footing widths from the overall dimensions. This creates the center pad dimensions. Check that both center dimensions remain positive. Small pads may need a narrow footing.
Describe the Sloped Edge
Enter the footing depth beside the center pad. Then enter the depth at the outside edge. The outer depth should equal or exceed the inner depth. The calculator treats the transition as a continuous straight slope. It uses a rectangular-ring integration method. This method accounts for growing perimeter dimensions across the footing width. A simple average depth can understate or overstate volume.
Add Ordering Allowance
Fresh concrete is difficult to return once delivered. Include an overage for uneven excavation, spillage, and finishing losses. Many projects use five to ten percent. Complex forms may need more. Keep the allowance reasonable. Excess material adds cost and disposal work. Confirm local ready-mix minimums before placing an order.
Review Delivery Details
Bag yield and truck capacity convert volume into purchasing quantities. Enter the actual yield printed on the bag. Enter the supplier's usable truck capacity. Concrete suppliers may limit partial loads. Add a price per delivery unit for an estimated material cost. Taxes, short-load charges, pumping, and labor remain separate. Verify these figures with your supplier.
Check Before Pouring
Recheck field dimensions after forms are installed. Measure diagonal corners for square layouts. Confirm footing depths at several locations. Verify reinforcement, cover, anchors, and embedded items before ordering. Schedule enough workers for placement and finishing. Keep curing materials ready. This calculator provides planning values only. A qualified designer must confirm structural requirements and local code compliance.
Common questions
Frequently Asked Questions
1. Do overall dimensions include the footing?
Yes. Enter the length and width at the outside footing edge. The calculator subtracts two footing widths to determine the center pad dimensions.
2. Why are inner and outer footing depths needed?
They define the sloped perimeter profile. The inner depth starts beside the pad. The outer depth finishes at the footing edge. Their difference creates the slope.
3. Can the outer footing depth equal the inner depth?
Yes. Use matching depths for a level thickened perimeter. The formula then calculates a uniform-depth footing ring instead of a slope.
4. Does the calculation include a pedestal?
Yes, when you enter pedestal length, width, and height. Leave all three pedestal fields at zero when the pad has no raised pedestal.
5. How much overage should I use?
Five to ten percent suits many simple pours. Use more when excavation varies, access is difficult, or forms are irregular. Avoid excessive overage without a disposal plan.
6. What bag yield should I enter?
Use the usable concrete yield printed by the manufacturer. Do not enter the bag weight. Yield is normally listed in cubic feet or litres.
7. Why does the truck estimate round upward?
A partial truck cannot be counted as a fraction of a delivery. The calculator rounds upward, so the estimated capacity covers the full order volume.
8. Does the cost include pumping or short-load fees?
No. The material estimate multiplies ordered volume by your entered unit price. Add delivery, pumping, taxes, labor, and supplier fees separately.
9. Can I enter metric dimensions?
Yes. Select Metric first. Use metres for plan dimensions, millimetres for depths, litres for bag yield, and cubic metres for truck capacity.
10. Does this replace engineering design?
No. It estimates concrete volume only. A qualified professional should verify soil conditions, reinforcement, footing dimensions, loads, drainage, and local requirements.
11. What happens when the footing is too wide?
The calculator stops and shows an error if the footing leaves no center pad area. Reduce the footing width or increase the overall footprint.
Planning estimate only. Confirm dimensions, structural design, delivery constraints, and applicable requirements before ordering concrete.