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.
Comment utiliser ce calculateur
- Saisissez vos dimensions — pieds pour les longueurs, pouces pour l'épaisseur.
- Ajustez les options — pourcentage de perte, taille du sac et prix local du béton.
- Lisez vos résultats — le volume, les sacs, le poids et le coût se mettent à jour en direct.
La formule
Octagon volume = 2 × (1 + √2) × side² × thickness ≈ 4.828 × side² × thickness Exemple résolu : 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.
Foire aux questions
Questions courantes sur le 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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