Tee Calculator Formula

This tee calculator works out the total amount of concrete needed to fill a tee-shaped footing or slab. You enter the dimensions of the stem (the vertical part) and the base (the horizontal part), and it returns the total volume in cubic yards and cubic meters.

Formula

The volume of a tee-shaped footing is the sum of the volumes of its two rectangular parts: the stem (vertical web) and the base (horizontal flange). The formula is:

V = (t × h + b × B) × L

• V = total volume (ft³ or m³)
• t = stem thickness (in or mm)
• h = stem height (ft or m)
• b = base width (ft or m)
• B = base thickness (ft or m)
• L = total length of the footing (ft or m)

All dimensions must be in the same unit system. If you mix inches and feet, convert first (e.g., 12 inches = 1 foot).

Worked Example

Using the default values from the calculator:

• Stem thickness (t) = 12 in = 1 ft
• Stem height (h) = 3 ft
• Base width (b) = 2 ft
• Base thickness (B) = 1 ft
• Length (L) = 20 ft

Step 1: Cross-sectional area of the stem = t × h = 1 ft × 3 ft = 3 ft²

Step 2: Cross-sectional area of the base = b × B = 2 ft × 1 ft = 2 ft²

Step 3: Total cross-sectional area = 3 ft² + 2 ft² = 5 ft²

Step 4: Volume = area × length = 5 ft² × 20 ft = 100 ft³

Step 5: Convert to cubic yards: 100 ft³ ÷ 27 = 3.70 yd³ (rounded to 2 decimals)

The calculator shows exactly 3.70 yd³ for the first output, confirming the formula.

When to Use a Tee Footing

Tee-shaped footings are common in concrete construction for retaining walls, foundation walls, and some bridge abutments. The stem is the vertical wall portion, and the base spreads the load over a wider area of soil. This shape provides resistance to overturning and sliding, which is why it is used where lateral earth pressure is a concern.

The formula assumes the footing is a uniform shape along its entire length. If the footing has openings, steps, or changes in dimension, you must divide it into simpler shapes and calculate each separately.

How to Read the Result

The calculator gives three outputs:

• Total volume (ft³) – the raw cubic footage, useful for estimating concrete in small quantities.
• Cubic yards (yd³) – the standard unit for ordering ready-mix concrete in the US. Always order a little extra (5–10%) to account for spillage, uneven subgrade, or over-excavation.
• Cubic meters (m³) – the metric equivalent, used in most countries outside the US.

For example, a 3.70 yd³ footing would require about 3.9 yd³ of concrete when you add a 5% waste factor.

Common Mistakes and How to Avoid Them

• Mixing units: Using inches for stem thickness and feet for length is the most frequent error. Convert everything to the same unit before multiplying.
• Forgetting to convert to yards: Concrete is ordered by the cubic yard, not cubic feet. Divide cubic feet by 27.
• Ignoring the length: The formula multiplies the cross-sectional area by the total length. If you have a 20-foot wall, the volume is 20 times the area of one cross-section.
• Rounding too early: Round only at the final step. If you round the area to 5 ft² and then multiply, you get the same result, but rounding intermediate values in more complex shapes can cause errors.

Limits of the Formula

This formula assumes perfectly rectangular cross-sections. Real-world footings may have chamfered edges, rebar, or irregular subgrades. The volume of rebar is usually negligible, but if you need extreme accuracy, subtract the displaced volume of large anchor bolts or embedded items.

The formula also does not account for concrete shrinkage, settlement, or waste. For ordering purposes, add 5–10% to the calculated volume. For structural design, consult an engineer who can verify soil bearing capacity and reinforcement requirements.

Alternatives to a Tee Footing

If you are designing a foundation, you might consider other shapes:

• Rectangular footing: Simpler to form and pour, but less efficient for resisting overturning.
• Inverted tee (IT) footing: The base is wider at the bottom, providing more bearing area. The formula is the same, just with the base dimensions swapped.
• Spread footing: A wider base that distributes load over more soil, often used for columns.
• Pile cap: Used when soil is weak; piles transfer load to deeper, stronger layers.

Each has its own design considerations. The tee shape is a good middle ground between material efficiency and construction simplicity.

Frequently Asked Questions

What is the difference between a tee footing and an inverted tee footing?

A tee footing has the stem on top of the base, like a T. An inverted tee has the stem below the base, like an upside-down T. The volume calculation is the same because the cross-sectional area is the same; only the orientation changes.

How do I calculate concrete for a tee footing with a step?

Divide the footing into two rectangular prisms at the step, calculate each volume separately, and add them together. For example, if the stem height changes from 3 ft to 4 ft halfway along the length, calculate the volume for each segment with its own height.

Should I order extra concrete beyond the calculated volume?

Yes, always order 5–10% more than the calculated volume. The subgrade may be uneven, forms may bulge, or concrete may be spilled during placement. It is cheaper to have a little extra than to run short and pay for a second delivery.

Can I use this formula for a tee-shaped slab on grade?

Yes, the same volume calculation applies to any tee-shaped prism. The formula only cares about the cross-sectional area and length, not whether it is a footing or a slab. Just make sure all dimensions are in the same units.

What if my tee footing has a different length on the stem and base?

In a typical tee footing, the stem and base run the same length. If they differ, you must calculate the stem and base as two separate rectangular prisms: (stem thickness × stem height × stem length) + (base width × base thickness × base length).

How do I convert cubic yards to bags of concrete?

A standard 80-pound bag of concrete mix yields about 0.6 cubic feet. One cubic yard is 27 cubic feet, so you need about 45 bags per cubic yard. For 3.70 yd³, that would be about 167 bags. Ready-mix concrete is usually more practical for large footings.

Related

• Taylor Polynomial Calculator: How It Works
• Zeros of Polynomial Functions Calculator
• Quadratic Factoring Calculator: Steps & Examples

in t | Stem thickness | in | 12 | 0
in h | Stem height | ft | 3 | 0
in b | Base width | ft | 2 | 0
in B | Base thickness | ft | 1 | 0
in L | Length | ft | 20 | 0
out vol_ft3 | Total volume | ft³ | (t/12 * h + b * B) * L | 2
out vol_yd3 | Cubic yards | yd³ | vol_ft3 / 27 | 2
out vol_m3 | Cubic meters | m³ | vol_ft3 * 0.0283168 | 2