Measure The Edge Before You Estimate The Concrete
Use this Concrete Perimeter Calculator to calculate the perimeter of rectangular, square, custom multi-side and circular concrete projects. You can also convert a known perimeter into concrete volume for continuous footings, perimeter strips, curbs, grade edges and similar linear concrete elements by entering the planned width and depth.
Calculate rectangle, custom polygon or circular perimeter, or convert known perimeter length into concrete volume and approximate material cost.
Enter finished length and width to calculate perimeter, linear feet and optional area.
Finished outside length
Finished outside width
Perimeter is a geometric measurement only. It does not determine structural footing, reinforcement, slab thickness, joint spacing or code requirements.
Enter up to eight boundary lengths. Leave unused sides blank.
Calculate circumference from diameter for circular slabs, pads, tanks, rings and round foundations.
Convert a known perimeter into concrete volume for a continuous footing, curb, edge strip or similar uniform linear element.
This mode is a material quantity calculator, not a footing, curb or structural design tool. Use the dimensions specified for the project. Verify reinforcement, bearing, frost depth, drainage and applicable code requirements separately.
A Concrete Perimeter Calculator measures the total distance around a concrete project. For a rectangle or square, the calculator adds all four sides. For a circle, it calculates circumference from the diameter. For an irregular boundary, it adds the individual side lengths entered by the user. The result is a linear measurement in feet, not a volume.
That distinction matters because perimeter is often used during concrete planning for forms, edge reinforcement, continuous footings, curbs and grade beams. A 100-foot perimeter does not tell you how many cubic yards of concrete are required until the cross-sectional width and depth of the concrete element are also known. The fourth calculator mode combines linear length with a rectangular cross-section to estimate cubic feet and cubic yards.
For a square where all sides are equal, the same formula simplifies to four times the side length.
The diameter is the straight-line distance across the circle through its center.
Width and depth are converted from inches to feet before calculating volume.
Measure the total outer edge of rectangular slabs, patios, driveways and pads.
Add individual side lengths when a project does not form a simple rectangle.
Calculate circumference for circular pads, rings, tanks and round foundations.
Convert perimeter length into cubic yards when width and depth are uniform.
Perimeter, area and volume describe three different parts of a project. Perimeter measures the boundary in linear feet. Area measures the surface in square feet. Volume measures the three-dimensional amount of concrete in cubic feet or cubic yards. One dimension cannot replace another.
For example, a 30 ft × 20 ft slab has a perimeter of 100 linear feet and an area of 600 square feet. If the slab itself is 4 inches thick, its flat slab volume is based on 600 square feet × 4 inches. If there is also a continuous 12-inch-wide by 8-inch-deep perimeter footing, that footing volume is calculated separately from the 100 linear feet around the slab.
| Measurement | Unit | What It Describes | Concrete Planning Example |
|---|---|---|---|
| Perimeter | ft | Distance around the edge | Forms, curb length, continuous footing length |
| Area | ft² | Surface coverage | Slab footprint, sealer or finishing area |
| Volume | ft³ / yd³ | Three-dimensional quantity | Ready-mix or bagged concrete quantity |
If you need surface-area takeoff rather than boundary length, use the Concrete Square Foot Calculator. For full-project material volume, use the Concrete Calculator.
Measure the actual finished edge of the concrete element whenever possible. For new work, that may be the inside face of forms or the planned finished dimension shown on drawings. For existing concrete, measure along the real outer boundary. Do not automatically use excavation dimensions because excavation can extend beyond the finished concrete for formwork, working room, drainage or base preparation.
Decide exactly which concrete edge you are measuring.
Separate irregular shapes into straight measurable boundary segments.
Record each finished side length using consistent units.
Use the rectangle formula or sum every custom side.
If calculating volume, enter the specified width and depth separately.
Add length and width: 30 + 20 = 50. Multiply by 2 to include the opposite sides. The perimeter is 100 linear feet. The slab area is 600 square feet, but perimeter and area serve different estimating purposes.
A square has four equal sides, so 18 × 4 = 72 feet of perimeter. You can also use 2 × (18 + 18) and obtain the same result.
Circumference is π × diameter. A 12-foot diameter circle has a perimeter of approximately 37.70 feet. Its surface area is approximately 113.10 square feet.
Assume a uniform strip is 12 inches wide and 8 inches deep. Convert 12 inches to 1 foot and 8 inches to approximately 0.667 foot. The exact geometric volume is approximately 66.67 cubic feet, or 2.47 cubic yards before an optional ordering allowance.
A building footprint is sometimes used as an early way to estimate the length of a continuous perimeter footing. If the footing follows the entire outside edge of a simple rectangular structure, the building perimeter can provide the linear length. Material volume still depends on the actual footing width and depth shown by the project design.
Do not assume a standard footing width or depth from this calculator. Footing dimensions can depend on structural loads, soil bearing capacity, frost conditions, wall type, reinforcement, local building requirements and engineering. Interior strip footings, isolated pads, thickened slab edges and grade beams must be added separately if they are not part of the outside perimeter.
For footing-specific geometry and quantities, use a dedicated Concrete Footing Calculator where appropriate. For reinforcement quantity planning, use the Concrete Rebar Quantity Calculator.
Curbs, mow strips, border strips and perimeter grade edges are linear concrete elements. When the cross-section is rectangular and uniform, their volume can be estimated by multiplying total length by width and depth. More complex curb profiles may not be rectangular, and their cross-sectional area should be calculated from the actual shape before multiplying by length.
Openings and interruptions also matter. If a curb runs around only three sides of a slab, do not use the full slab perimeter. If a driveway entrance creates a 12-foot break in a continuous curb, subtract that opening from the measured curb length before calculating volume.
Start with linear feet around the project, then add the concrete cross-section when estimating material quantity.
The amount of concrete per linear foot is controlled by the cross-sectional dimensions. A wider or deeper footing uses more concrete even when the perimeter length remains exactly the same. The values below are mathematical volume examples only and are not recommended footing or curb dimensions.
| Example Cross-Section | Volume per Linear Foot | Approx. yd³ per 100 ft | Important Note |
|---|---|---|---|
| 8 in × 8 in | Approx. 0.444 ft³ | Approx. 1.65 yd³ | Geometry example only |
| 12 in × 8 in | Approx. 0.667 ft³ | Approx. 2.47 yd³ | Geometry example only |
| 12 in × 12 in | 1.000 ft³ | Approx. 3.70 yd³ | Geometry example only |
| 16 in × 8 in | Approx. 0.889 ft³ | Approx. 3.29 yd³ | Geometry example only |
| 18 in × 12 in | 1.500 ft³ | Approx. 5.56 yd³ | Geometry example only |
A clean plan dimension describes ideal geometry. Field conditions can produce a different finished boundary or volume. Form thickness, offsets, recesses, steps, corners, construction joints, wall returns and local excavation can change the amount of concrete placed. For continuous footings, excavation depth may vary if the subgrade is uneven.
The calculator therefore separates geometric perimeter from optional material-volume planning. Verify the actual formed dimensions before placing the final concrete order.
Perimeter length is useful when estimating the quantity of form material around a slab or continuous footing. A 100-foot rectangular slab perimeter may require approximately 100 linear feet of outside form contact, but real form takeoff can be higher because of laps, cuts, stakes, bracing, returns and internal formed edges.
Reinforcement takeoff should also be handled separately. A perimeter length does not automatically equal rebar length because lap splices, hooks, development, corners, bar layers and tie spacing affect the total. Use the Concrete Rebar Calculator or Concrete Rebar Quantity Calculator for material planning based on the actual reinforcement layout.
Foundation and retaining-wall projects can include multiple concrete components: footings, walls, pilasters, keys, grade beams and slabs. The perimeter of the building or wall line may help establish one linear dimension, but each component needs its own cross-section or volume calculation.
For wall projects, use the Concrete Retaining Wall Calculator or the general Concrete Calculator to estimate wall volume. The perimeter calculator is most useful when the concrete element follows a continuous boundary with a uniform cross-section.
Perimeter is easy to convert between feet and meters because it is a linear measurement. One international foot equals exactly 0.3048 meter. This calculator reports approximate meters alongside feet so project dimensions can be checked against metric drawings or supplier documents.
The U.S. National Institute of Standards and Technology provides official SI and measurement guidance. See the NIST SI Units – Length resource for measurement information.
A perimeter calculator should not be used to decide footing width, footing depth, reinforcement, bearing capacity or frost protection. Those are design and construction questions. ACI publishes structural concrete codes and guidance that address concrete design and construction requirements far beyond geometric quantity calculations.
For structural work, consult the project drawings, specifications and qualified design professionals as required. ACI's Building Code Requirements for Structural Concrete (ACI 318) is an authoritative structural-concrete reference. The calculator on this page only performs geometry and quantity conversions from dimensions supplied by the user.
Common questions about concrete perimeter, linear feet, circular boundaries and perimeter concrete volume.