Concrete Needed
0.341 cu ft
Volume
589 cu in
Weight
51.1 lbs
60lb Bags
1
Retail concrete planters typically cost $25–$100+ depending on size and finish.
Inputs
Result
Outer volume = π × 6² × 10 = 1,131 cu in. Inner volume = π × 4.5² × 8.5 = 541 cu in. Concrete = 1,131 - 541 - 1.2 (drainage) = 589 cu in. At 150 lb/cu ft: ~41 lbs.
Inputs
Result
Outer volume = 12 × 12 × 10 = 1,440 cu in. Inner = 9 × 9 × 8.5 = 688.5 cu in. Concrete = 1,440 - 688.5 = 751.5 cu in ≈ 0.435 cu ft. Needs 1 bag (0.45 cu ft capacity).
The amount depends on planter shape, size, and wall thickness. A 12-inch diameter cylinder planter that is 10 inches tall with 1.5-inch walls needs about 475 cubic inches (0.27 cu ft) of concrete, or roughly 1 bag of 60-pound mix. Larger planters or thicker walls require proportionally more.
| Size (Dia × H) | Wall | Concrete | 60 lb Bags |
|---|---|---|---|
| 8" × 8" | 1" | 0.08 cu ft | 1 |
| 12" × 10" | 1.5" | 0.27 cu ft | 1 |
| 16" × 12" | 2" | 0.64 cu ft | 2 |
| 20" × 14" | 2" | 1.1 cu ft | 3 |
Use a sand/topping mix or Portland cement with fine sand for small planters (under 12"). Standard premix (Quikrete, Sakrete) works for larger planters. Avoid gravel-heavy mixes for thin-walled planters as the aggregate creates rough textures and weak spots.
Concrete weighs about 150 pounds per cubic foot. A 12-inch cylinder planter with 1.5-inch walls weighs approximately 41 pounds empty. Always calculate weight before building large planters, especially for balconies, shelves, or elevated surfaces.
Yes, drainage holes are essential for plant health. Without drainage, water pools at the bottom and causes root rot. Drill or mold a 1/2-inch to 1-inch hole in the bottom center. For large planters, add 2–3 drainage holes spaced evenly.
Concrete reaches working strength in 24–48 hours but takes 7–28 days to fully cure. Remove from the mold after 24–48 hours. Keep moist (cover with plastic or mist daily) for 5–7 days for best strength. Wait at least 7 days before adding soil and plants.
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Last Updated: Mar 9, 2026
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