Volume, bags and cost for a slab or footing — waste included
Enter a valid length
Enter a valid width
Enter a valid thickness
Enter a waste allowance (0-50)
Enter a valid price
Concrete punishes guesswork in both directions: order too little and the pour stops mid-job, leaving a cold joint that never bonds properly; order too much and you pay for surplus you must dump. This calculator sizes a slab or footing precisely — volume first, then a waste allowance, then what that means in ready-mix cost or bagged mix.
Enter the slab's length and width plus its thickness, in feet/inches or metres/centimetres. You get the base volume in cubic yards (or cubic metres), the volume after your chosen waste allowance, the estimated cost at your price per yard, and the equivalent count of bagged mix — 40-lb and 80-lb bags, or 25-kg bags in metric.
A 40-lb bag yields about 0.011 yd³ (an 80-lb bag 0.022; a 25-kg bag ≈ 0.0104 m³). The waste allowance exists because the subgrade is never perfectly level — a 10% cushion is standard for slabs on ground.
A 20 × 10 ft patio at 4 inches thick: 20 × 10 × 0.333 ft = 66.7 ft³ ÷ 27 = 2.47 yd³. With 10% waste: 2.72 yd³. At $160/yd³ delivered, about $435 — versus roughly 247 of the 40-lb bags, which at $6 each cost more like $1,480 plus a full day of mixing. Past about a yard, ready-mix wins on price and on your back.
| Project | Size | Thickness | Volume + 10% |
|---|---|---|---|
| Patio | 20 × 10 ft | 4 in | 2.72 yd³ |
| Shed base | 8 × 6 ft | 4 in | 0.65 yd³ |
| Driveway pad | 20 × 10 ft | 6 in | 4.08 yd³ |
| Garden path | 6 × 3 m | 10 cm | 1.98 m³ |
One more habit worth keeping: whatever the calculator says, tell the ready-mix plant the figure including waste and round up to their delivery increment — a quarter-yard extra is cheap insurance against a cold joint.
混凝土最怕拍脑袋：订少了浇到一半断料，留下永远结合不好的冷缝；订多了多花钱还得处理余料。这个计算器把地坪或条基的用量算准——先算方量，再留损耗，最后折算成商混费用或袋装袋数。
输入地坪的长、宽、厚度（英尺/英寸或米/厘米）。你会得到：基本方量（立方码或立方米）、计入损耗后的方量、按你填的单价折算的预估费用，以及等效的袋装水泥袋数——40 磅与 80 磅袋，公制为 25 公斤袋。
一袋 40 磅装约出方 0.011 立方码（80 磅装 0.022；25 公斤装约 0.0104 立方米）。损耗预留是因为基层永远不会绝对平整——地坪通常留 10%。
20 × 10 英尺、厚 4 英寸的庭院地坪：20 × 10 × 0.333 ft = 66.7 ft³ ÷ 27 = 2.47 立方码。计入 10% 损耗为 2.72 立方码。按商混 160 元/立方码算约 435 元——而用 40 磅袋装要约 247 袋，每袋 6 元就是 1,480 元上下，还得自己拌一整天。超过 1 立方码的活，商混在价格和腰上都完胜。
| 项目 | 尺寸 | 厚度 | 方量 +10% |
|---|---|---|---|
| 庭院地坪 | 20 × 10 英尺 | 4 英寸 | 2.72 立方码 |
| 棚屋基础 | 8 × 6 英尺 | 4 英寸 | 0.65 立方码 |
| 车道垫层 | 20 × 10 英尺 | 6 英寸 | 4.08 立方码 |
| 园路 | 6 × 3 米 | 10 厘米 | 1.98 立方米 |
再留一个习惯：无论计算器算出多少，向商混站报数时带上损耗并向上凑到他们的发货步长——多半方余量，是对付冷缝最便宜的保险。
Volume = length × width × thickness, converted to cubic yards (feet and inches: L × W × thickness-in-inches ÷ 12 ÷ 27). A 20 × 10 ft patio at 4 inches needs 20 × 10 × 0.333 ÷ 27 ≈ 2.47 cubic yards — order about 2.7 with a 10% allowance.
Walkway and patio slabs are typically 4 inches; driveways 5–6 inches with reinforcement; footing strips 8–12 inches depending on load and soil. When in doubt, local building code wins.
About 90 bags of the 40-lb kind, 60 bags at 60 lb, or 45 at 80 lb — a cubic yard is roughly 4,000 lb of mix. Bagged concrete suits small jobs; past about a cubic yard, ready-mix delivery is cheaper and far faster than mixing by hand.
Last reviewed: October 5, 2026 · How we calculate · Sources: Portland Cement Association, ACI 318
最近复核：2026 年 10 月 5 日 · 我们的计算方法 · 来源：波特兰水泥协会 (PCA)、ACI 318 规范