Concrete Bag Calculator
Choose the pour shape, enter dimensions, select a bag size (or custom yield), and get the bag count to order — including a waste margin for real-world pours.
Calculate
Calculate
Measurements convert when you switch units
Result
The formula
First compute pour volume (slab L×W×D, column πr²h, or wall L×H×T). Apply waste, then divide by the bag’s wet yield and round up to whole bags.
Worked example
- Slab 2 m × 1 m × 0.1 m → base volume 0.2 m³
- Add 10% waste → order volume 0.22 m³
- 25 kg bags at 12.5 L (0.0125 m³) yield → ceil(0.22 ÷ 0.0125) = 18 bags
Result: Order 18 bags of 25 kg mix
How concrete bag quantity is calculated
This tool converts project geometry into wet concrete volume, then translates that volume into bag counts using the manufacturer yield for your bag size.
Volume comes first
Slab volume is length × width × depth. A circular column or pier uses π × radius² × height. A wall uses length × height × thickness. Keep every dimension in the same unit system.
Bag yield, not bag weight
Bags are sold by weight (25 kg, 40 kg, 60 lb, 80 lb), but the useful number is wet yield — how much placed concrete one bag produces after mixing. Always prefer the yield printed on your product bag or datasheet.
Why waste is added
Uneven subgrade, form bulging, spillage, and rounding mean the theoretical volume understates what you mix. A 5–10% waste factor is typical for small DIY pours; use more for rough grades or complex forms.
Rounding up
Partial bags are not useful mid-pour. The calculator always rounds up so you do not run short after the mixer is already wet.
What we do not model
No rebar displacement, no slump loss from delay, no specialty lightweight or high-strength mix densities, and no ready-mix truck logistics. For large pours, compare bag cost and labour against a ready-mix delivery.
Interesting facts
Yield beats bag weight for ordering
Two 25 kg bags from different brands can yield different volumes. Ordering from weight alone without the label yield is a common way to underbuy.
Typical 60 lb and 80 lb US bag yields
Many general-purpose US bagged mixes list about 0.45 ft³ for a 60 lb bag and about 0.60 ft³ for an 80 lb bag. Confirm on the package you buy.
Metric bags often quote litres
European and other metric bags frequently publish yield in litres (for example ~12.5 L for a common 25 kg general-purpose bag). Convert litres to m³ by dividing by 1000.
Small pours favour bags; large pours favour trucks
Bag mixing is practical for pads, fence posts, and small slabs. Once you need multiple cubic metres, ready-mix usually wins on labour and consistency.
Water content changes strength
Adding extra water to stretch a bag increases volume slightly but weakens the mix. Follow the bag’s water guidance instead of watering for yield.
Cold joints risk on slow bag pours
If mixing and placing take too long, sections can set before the next batch. Plan crew size and bag count so continuous placement is realistic.
Frequently asked questions
Compute slab volume (length × width × depth), add waste, then divide by the bag yield. Example: 2 × 1 × 0.1 m = 0.2 m³; with 10% waste and 0.0125 m³ yield → 18 bags.
One cubic yard is 27 ft³. At ~0.60 ft³ per 80 lb bag, you need about 45 bags before waste (27 ÷ 0.60). Add your waste factor and round up.
Use the 60 lb preset (about 0.45 ft³ / ~12.7 L yield), enter your dimensions, and calculate. Always verify the yield on your specific brand.
If each bag yields 12.5 L (0.0125 m³), you need 80 bags per m³ before waste (1 ÷ 0.0125). With 10% waste, plan on 88 bags.
Use wet yield for quantity. Weight tells you how heavy each bag is to lift and transport, not how much volume you will place.
Simple, well-formed pads often use 5%. Uneven ground, post holes, and first-time DIY pours commonly use 8–10% or more.
Stick to one product and one bag size when possible so water ratios and set times stay consistent. If you must mix sizes, calculate each yield separately and add the bag counts.
If the order volume is large (often above roughly 0.5–1 m³ / ~0.7–1.3 yd³) or you need continuous placement, ready-mix is usually faster and more consistent than bag mixing.
No. Bagged concrete mix already includes cement and aggregates. Use separate sand or gravel calculators only if you are designing a site-mixed recipe from bulk materials.
References
- Concrete fundamentals and practice Industry standards and guidance for concrete materials and placement.
- Metric (SI) units guidance Unit conversions between cubic metres, litres, and customary volume units.
- Cement and concrete overview General reference on cementitious materials and concrete applications.