Planning a new outdoor storage project requires more than just picking a spot in the backyard. This storage shed calculator helps you determine the physical footprint, the total usable volume, and the material requirements for your foundation. Whether you are building a DIY wooden shed or purchasing a pre-fab resin unit, knowing your dimensions is the first step toward organized storage.
Understanding the Measurements
Floor Area: This is the total square footage on the ground. It determines how many large items (like lawnmowers or ATVs) you can park.
Total Volume: Unlike floor area, volume considers the height. This is crucial if you plan to install shelving or hang tools from the rafters.
Peak vs. Wall Height: Most sheds have a gabled or sloped roof. The wall height is the vertical space before the roof starts, while the peak height is the tallest point. Our calculator uses both to find the true cubic capacity.
Example Calculation
If you plan to build a standard 10′ x 12′ shed:
Floor Area: 10 ft × 12 ft = 120 sq. ft.
Foundation: A 4-inch concrete slab would require approximately 1.48 cubic yards of concrete.
Volume: With 7-foot walls and a 9-foot peak, you would have roughly 960 cubic feet of storage space.
Choosing the Right Size for Your Needs
Before finalizing your shed purchase, consider these common usage tiers:
Shed Size
Best For
Small (4×6 to 6×8)
Push mowers, garden tools, and vertical bike storage.
Medium (8×10 to 10×12)
Riding mowers, workbenches, and seasonal holiday decor.
Large (12×16+)
Small vehicles, workshops, or "she-shed"/"man-cave" conversions.
function calculateShed() {
var length = parseFloat(document.getElementById('shedLength').value);
var width = parseFloat(document.getElementById('shedWidth').value);
var wallHeight = parseFloat(document.getElementById('shedWallHeight').value);
var peakHeight = parseFloat(document.getElementById('shedPeakHeight').value);
var thickness = parseFloat(document.getElementById('slabThickness').value);
if (isNaN(length) || isNaN(width) || isNaN(wallHeight) || isNaN(peakHeight) || isNaN(thickness)) {
alert("Please enter valid numbers for all fields.");
return;
}
if (peakHeight < wallHeight) {
alert("Peak height cannot be lower than wall height.");
return;
}
// 1. Calculate Area
var area = length * width;
// 2. Calculate Volume (Rectangular prism + Triangular prism for gabled roof)
var baseVolume = area * wallHeight;
var roofVolume = area * (peakHeight – wallHeight) * 0.5;
var totalVolume = baseVolume + roofVolume;
// 3. Concrete Slab (in cubic yards)
// Formula: (Area * (thickness/12)) / 27
var concreteYards = (area * (thickness / 12)) / 27;
// 4. Box Capacity Estimate
// Assume a "Large Box" is roughly 4.5 cubic feet (24"x18"x18")
// Use 70% efficiency for realistic stacking
var boxCapacity = Math.floor((totalVolume * 0.7) / 4.5);
// Update Display
document.getElementById('areaResult').innerText = area.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 2});
document.getElementById('volumeResult').innerText = totalVolume.toLocaleString(undefined, {minimumFractionDigits: 0, maximumFractionDigits: 2});
document.getElementById('concreteResult').innerText = concreteYards.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('boxResult').innerText = boxCapacity.toLocaleString();
// Contextual Advice
var adviceText = "";
if (area = 50 && area <= 120) {
adviceText = "A mid-sized shed. Ideal for riding mowers and potentially a small workbench.";
} else {
adviceText = "This is a large structure. Ensure you check local zoning laws for permits on buildings over 120 sq ft.";
}
document.getElementById('sizeAdvice').innerText = adviceText;
document.getElementById('shedResult').style.display = 'block';
}