Enter your roll's outer diameter, inner diameter (core), and material thickness to calculate the total length of material wound on the roll. Works for carpet, tape, paper, plastic film, and any other rolled sheet material. Choose between imperial (inches/feet) or metric (mm/m) units.
Roll Length
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Roll Length (alternate unit)
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Number of Turns / Wraps
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Cross-Section Area of Material
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Measure three values from your roll: the outer diameter of the entire roll, the inner diameter of the hollow core (the tube in the center), and the thickness of the sheet material itself. Enter these three values into the calculator along with your preferred unit system, and the calculator instantly gives you the total length of material wound on the roll.
The formula used is: Length = π × (OD² − ID²) / (4 × thickness), where OD is the outer diameter, ID is the inner diameter, and thickness is the material thickness. This is derived from the difference in cross-sectional areas of the outer and inner circles, divided by the cross-sectional area of a single layer of material.
The cross-sectional area of the wound material equals π/4 × (OD² − ID²). Each layer of material contributes a cross-sectional area of thickness × length. Setting these equal and solving for length gives the formula. This approach is accurate as long as the material is wound uniformly and tightly.
The calculator assumes the material is wound uniformly with no gaps between layers, the material is incompressible (no stretching or squishing), the roll is perfectly cylindrical, and the thickness is constant throughout. For soft or elastic materials like foam or rubber, real-world results may vary slightly.
For very thin materials like plastic film or paper, you can measure a stack of multiple sheets with calipers and divide by the number of sheets to get an accurate single-layer thickness. Alternatively, manufacturer spec sheets typically list the caliper or gauge of the material.
Simply double the radius to get the diameter before entering it into the calculator. For example, if your outer radius is 6 inches, enter 12 as the outer diameter. The same applies to the inner (core) radius.
This calculator is set up to find the roll length from the diameters and thickness. To find the outer diameter from a known length, you would rearrange the formula: OD = √(ID² + 4 × thickness × length / π). You can use the known length and solve manually, or look for a roll diameter calculator.
Roll lengths vary widely by material. A standard roll of toilet paper is roughly 100–200 feet. A roll of duct tape is typically 50–60 yards. Carpet rolls are often 100 feet long. Industrial plastic film and paper mill rolls can be thousands of feet. This calculator works for any of these scenarios.