Octagon Concrete Calculator
This octagon concrete calculator sizes eight-sided pads — the classic gazebo and hot-tub base. Enter one side's length and the thickness; the regular-octagon area formula does the rest.
Cómo usar esta calculadora
- Introduzca sus dimensiones — pies para longitudes, pulgadas para el espesor.
- Ajuste las opciones — porcentaje de desperdicio, tamaño de la bolsa y el precio local del hormigón.
- Lea sus resultados — el volumen, las bolsas, el peso y el costo se actualizan en vivo mientras escribe.
La fórmula
Octagon volume = 2 × (1 + √2) × side² × thickness ≈ 4.828 × side² × thickness Ejemplo resuelto: A gazebo pad with 4 ft sides at 4 in: 4.828 × 16 × 0.333 = 25.7 ft³ ≈ 0.95 yd³.
A regular octagon's area is 4.828 × side² — bigger than most people guess. The concrete calculator octagon math assumes all eight sides equal, which matches prefab gazebo kits.
If you know the width across the flats instead of a side length, divide by 2.414 to get the side. A 10 ft across-flats octagon has 4.14 ft sides.
Octagonal forms are cut from straight lumber at 22.5° angles — order 10% waste, since the corner cuts generate offcuts and the forms rarely close perfectly on the first try.
Preguntas frecuentes
Preguntas comunes sobre la octagon concrete calculator.
How much concrete for an octagon pad?
4.828 × side² × thickness. A pad with 5 ft sides at 4 in needs 4.828 × 25 × 0.333 = 40.2 ft³ ≈ 1.49 yd³.
I know the width, not the side — what now?
Divide the across-flats width by 2.414. A 12 ft-wide octagon has sides of 4.97 ft.
What angle do I cut octagon forms?
22.5° at each of the eight corners (forms meet at 135° interior angles).
How thick for a hot tub pad?
4 inches minimum, 6 inches for large spas — a filled hot tub can exceed 5,000 lb, so confirm bearing with the spa's spec sheet.
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