Calculate asphalt quantity for circular, semicircular, quarter circle, or annular ring (donut) pavement areas. Perfect for roundabouts, cul-de-sacs, and parking bays.
Supports full circles, semicircles, quarter circles, and annular rings (donut shapes with inner and outer radius).
Ideal for roundabouts (annular ring shape), cul-de-sacs (full circle), and curved parking bay areas.
Results include area (m²), volume (m³), total mix weight (tonnes), bitumen required, and optional cost estimate.
Enter radius and thickness to calculate
Typical dimensions for roundabouts, cul-de-sacs, and circular paved areas.
| Application | Shape | Typical Outer Radius | Typical Inner Radius |
|---|---|---|---|
| Mini roundabout | Annular ring | 6–8 m | 1–2 m |
| Standard roundabout | Annular ring | 10–15 m | 4–6 m |
| Large roundabout | Annular ring | 20–30 m | 8–15 m |
| Cul-de-sac | Full circle | 7–10 m | — |
| Circular parking bay | Full circle | 4–6 m | — |
| Curved access ramp | Quarter circle | 5–12 m | — |
All circular calculations derive from the standard circle area formulas using π (pi = 3.14159). The tonnage formula then multiplies the area by thickness and density — identical to rectangular calculations but with a circular area input.
A roundabout with outer radius R = 12 m and central island inner radius r = 5 m, 50 mm AC 14 wearing course at 2,350 kg/m³. Area = π × (12² − 5²) = π × (144 − 25) = 3.14159 × 119 = 373.9 m². Weight = 373.9 × 0.050 × 2,350 ÷ 1,000 = 43.9 tonnes. Add 5% waste = order 46.1 tonnes.
A residential cul-de-sac turnaround with radius = 8 m, 75 mm total asphalt at 2,300 kg/m³. Area = π × 8² = 201.1 m². Weight = 201.1 × 0.075 × 2,300 ÷ 1,000 = 34.7 tonnes. For a two-coat design (50 mm base + 25 mm surface): calculate each layer separately with their respective mix densities. For the full project including connecting road, use the Road Asphalt Calculator.
Semicircles appear in curved driveway turnarounds, bus bay end treatments, and T-junction bell-mouths. Quarter circles appear in curved access ramp treatments and corner footpath crossings. Formula: Semicircle area = π × r² ÷ 2; Quarter circle = π × r² ÷ 4. For a 6 m radius semicircle at 50 mm: Area = 56.5 m², Weight = 56.5 × 0.050 × 2,350 ÷ 1,000 = 6.6 tonnes. Always add 5–10% for edge waste.
For irregular shapes combining curves and rectangles (e.g., a cul-de-sac with a straight access road), calculate the circular portion here and the rectangular road section using the Road Asphalt Calculator, then sum the tonnage results. This combined approach handles almost any complex pavement area without needing CAD software for material estimation.
Circular and curved pavement areas require a different calculation approach than rectangular projects — these are the three most common scenarios where this tool is essential.
Traffic engineers and civil contractors use this calculator to estimate asphalt tonnage for roundabout carriageways. A roundabout is an annular ring — the outer boundary is the kerb line and the inner boundary is the central island edge. Roundabouts typically require higher-spec asphalt (SMA or polymer-modified binder) due to the slow-speed turning and channelised steering stress that causes rapid rutting in standard HMA. Calculate tonnage by entering outer and inner radii and the wearing course thickness specified in the road authority standard.
Related: Asphalt Tonnage Calculator
Subdivision developers and residential paving contractors calculate asphalt quantities for cul-de-sac turnaround areas. A standard residential cul-de-sac has a full-circle paved radius of 7.5–10 m. For a 9 m radius at 75 mm total asphalt: 254.5 m² × 0.075 × 2,300 ÷ 1,000 = 43.9 tonnes. This is calculated separately from the connecting street tonnage and combined for the plant order. Use the Road Asphalt Calculator for the street section.
Related: Asphalt Cost Calculator
Commercial property developers estimate asphalt for curved parking lot features — circular feature bays, semicircular end treatments in parking aisles, and quarter-circle corner sweeps at driveway entries. These curved areas cannot be accurately quantified using the rectangular area calculator alone. By entering the radius and shape type here, then combining with the rectangular parking grid tonnage from the Square Metres Calculator, the full parking lot material order is accurately quantified.
Related: Square Metres Calculator
Select the circular shape that matches your project: full circle (cul-de-sac, roundabout centre, circular pad), semicircle (half-moon bay, curved driveway end), quarter circle (corner treatment), or annular ring (donut shape, for roundabouts with a central island). Each shape uses a different area formula to give you an accurate asphalt tonnage.
For full circles, semicircles, and quarter circles, enter the outer radius. For annular rings, enter both the outer radius and the inner radius (the exclusion zone). Input radius in metres or feet — select your preferred unit. Then enter the required compacted asphalt thickness in millimetres or inches. The area is calculated using π (3.14159).
The calculator displays both the geometric area (m² or sq ft) and the estimated asphalt tonnage. Verify the area figure makes physical sense before accepting the tonnage result — for a 5 m radius full circle you should see approximately 78.5 m². Add 5–10% to your material order for edge trimming and compaction variability before calling your asphalt plant.
For a cul-de-sac turnaround, use the full circle shape and enter the outer paved radius. For a roundabout with a raised central island, use the annular ring shape: the outer radius is the edge of the carriageway and the inner radius is the edge of the central island. Multiply the resulting area by your layer thickness and density to get the asphalt tonnage. Remember that roundabouts typically require heavier-duty asphalt (SMA or polymer-modified binder) due to slow-speed turning stresses.
The formulas are: Full circle = π × r²; Semicircle = (π × r²) ÷ 2; Quarter circle = (π × r²) ÷ 4; Annular ring = π × (R² − r²), where R is outer radius and r is inner radius. Volume is then area × thickness, and tonnage = volume × density. This calculator applies these formulas automatically — you just supply the radius and thickness values.
Measure the diameter (straight line across the widest point) and divide by 2 to get the radius. Alternatively, measure the circumference (distance around the edge) and divide by 2π (6.2832) to get the radius. For large roundabouts, satellite measurement tools in Google Maps or similar GIS applications allow you to measure the radius directly by placing a marker at the centre and measuring to the kerb line.
Yes — for a curved entry or parking bay that is approximately semicircular or quarter-circular in shape, select the matching shape type and enter the governing radius. For more complex shapes (e.g., a stadium car park with irregular curves), break the area into simpler geometric shapes — full or partial circles plus rectangles — and calculate each separately, then sum the individual tonnage results for your total order quantity.
Roundabouts experience high horizontal (turning) stresses from slow-moving vehicles steering around the central island — unlike straight roads where forces are primarily vertical. These turning stresses promote rutting and shoving in standard dense-graded HMA, particularly in the wheel paths around the roundabout. Most road authorities specify SMA (Stone Mastic Asphalt) or polymer-modified binder (PMB) for roundabout wearing courses for improved resistance to these stresses. SMA at 2,300–2,350 kg/m³ and 40–50 mm thickness is a common specification. Confirm the exact mix type with your local road authority before ordering. Use the Metric Calculator for detailed SMA quantity estimation.
Area = π × 10² = 3.14159 × 100 = 314.16 m². For a 50 mm wearing course at 2,350 kg/m³: 314.16 × 0.050 × 2,350 ÷ 1,000 = 36.9 tonnes. For a 75 mm total pavement depth: 314.16 × 0.075 × 2,350 ÷ 1,000 = 55.4 tonnes. Enter these values directly into the circular calculator above to verify and get the full results including bitumen and aggregate sub-quantities. Add 5–8% overage before ordering from the plant.
A typical residential cul-de-sac has a paved turnaround radius of 8–10 m (measured to the kerb). For a 9 m radius full circle at 75 mm total asphalt (2 lifts): Area = π × 81 = 254.5 m². Weight = 254.5 × 0.075 × 2,300 ÷ 1,000 = 43.9 tonnes. Add 5–8% overage = order 46–47 tonnes. This quantity is in addition to the connecting street asphalt — use the Road Asphalt Calculator for the street section and sum both quantities for the total subdivision road asphalt order. Council specifications for residential subdivisions typically specify 40–50 mm surface course over a 75–100 mm base course.