Boulder Weight Calculator

Boulder Weight Calculator

Granite (165 lbs/ft³) Limestone (155 lbs/ft³) Sandstone (145 lbs/ft³) Basalt (185 lbs/ft³) Quartzite (160 lbs/ft³) Slate (170 lbs/ft³)
Rectangular / Cube Spherical (Round) Ellipsoid (Oval/Irregular)

Estimated Weight

0 lbs
0 Tons
Volume: 0 ft³

How to Calculate Boulder Weight

Estimating the weight of a boulder is critical for landscaping projects, construction, and transportation planning. Because rocks are significantly denser than wood or water, even a relatively small boulder can exceed the towing capacity of a standard pickup truck.

The Science of Rock Density

The weight of a rock depends on its volume and its mineral composition (density). Most landscape rocks fall within the range of 145 to 185 pounds per cubic foot (lbs/ft³). Granite is one of the heaviest common rocks, while sandstone is generally lighter due to its porous nature.

Common Rock Densities

Rock Type Density (lbs/ft³)
Granite 165 – 175
Limestone 150 – 165
Sandstone 140 – 150
Basalt 180 – 190

Example Calculation

Suppose you have a round (spherical) granite boulder with a diameter of 3 feet.

  1. Find the Volume: The formula for a sphere is (4/3) × π × radius³. Radius is 1.5 ft. Volume ≈ 14.14 ft³.
  2. Apply Density: Granite is approx. 165 lbs/ft³. 14.14 × 165 = 2,333 lbs.
  3. Convert to Tons: 2,333 / 2,000 ≈ 1.17 Tons.

This "small" 3-foot boulder actually weighs more than a small car!

function updateInputs() { var shape = document.getElementById("boulderShape").value; var lengthDiv = document.getElementById("lengthDiv"); var widthDiv = document.getElementById("widthDiv"); var heightDiv = document.getElementById("heightDiv"); var labelL = document.getElementById("labelL"); var labelW = document.getElementById("labelW"); var labelH = document.getElementById("labelH"); if (shape === "spherical") { labelL.innerText = "Diameter (ft)"; widthDiv.style.display = "none"; heightDiv.style.display = "none"; } else if (shape === "rectangular") { labelL.innerText = "Length (ft)"; widthDiv.style.display = "block"; heightDiv.style.display = "block"; labelW.innerText = "Width (ft)"; labelH.innerText = "Height (ft)"; } else if (shape === "ellipsoid") { labelL.innerText = "Longest Axis (ft)"; widthDiv.style.display = "block"; heightDiv.style.display = "block"; labelW.innerText = "Width Axis (ft)"; labelH.innerText = "Shortest Axis (ft)"; } } function calculateBoulderWeight() { var density = parseFloat(document.getElementById("rockDensity").value); var shape = document.getElementById("boulderShape").value; var L = parseFloat(document.getElementById("dimL").value) || 0; var W = parseFloat(document.getElementById("dimW").value) || 0; var H = parseFloat(document.getElementById("dimH").value) || 0; var volume = 0; if (shape === "rectangular") { volume = L * W * H; } else if (shape === "spherical") { var radius = L / 2; volume = (4 / 3) * Math.PI * Math.pow(radius, 3); } else if (shape === "ellipsoid") { // Ellipsoid volume is 4/3 * PI * a * b * c where a,b,c are semi-axes volume = (4 / 3) * Math.PI * (L / 2) * (W / 2) * (H / 2); } var weightLbs = volume * density; var weightTons = weightLbs / 2000; document.getElementById("weightLbs").innerText = Math.round(weightLbs).toLocaleString() + " lbs"; document.getElementById("weightTons").innerText = weightTons.toFixed(2) + " Tons"; document.getElementById("volumeOutput").innerText = "Calculated Volume: " + volume.toFixed(2) + " cubic feet"; document.getElementById("boulderResult").style.display = "block"; }

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