Concrete Bag Calculator
Already know your volume in cubic yards or feet? This bag calculator works backwards: enter the volume and your bag size to get the exact number of pre-mix bags to buy, the total dry weight you will be hauling, and an estimate of the mixing water needed. It is the reverse of a volume calculator — built for the hardware-store trip, not the pour plan.
The waste-adjusted volume from your volume estimate.
80-lb bags are the best value; 40-lb bags are easier to carry.
Bags needed
45
- Total dry weight45 bags × 80 lb.
- 3,600lb
- Estimated mixing water≈ 0.7 gal per bag — add gradually.
- 31.5gal
- Estimated yieldMixed concrete the bags will produce.
- 27ft³
How it was calculated
- Bags: 27.00 ft³ ÷ 0.60 ft³ per 80-lb bag = 45.00 → 45 bags (rounded up).
- Dry weight: 45 × 80 lb = 3,600 lb.
- Water: 45 × 0.7 gal ≈ 31.5 gal — add about three-quarters first, then adjust.
- Tip: buy about 5% extra (48 bags total) so a short pour never stalls the job.
How it works
Bags = ceiling(volume in ft³ ÷ yield per bag). The ceiling matters: 45.1 bags means you buy 46, because half-opened bags cannot be ordered.
Dry weight is simply bags × bag weight — what you will load, haul and carry.
Mixing water uses a rule of thumb of about 0.7 gallons per bag. Real water demand varies with mix design, humidity and desired slump, so always add water gradually and stop at the right consistency.
Estimated yield (bags × yield per bag) is always equal to or slightly above your target volume — that small surplus is your real-world safety margin.
Worked examples
1 cubic yard with 80-lb bags
1 yd³ = 27 ft³. Bags = 27 ÷ 0.60 = 45 exactly, so 45 bags. Dry weight = 45 × 80 = 3,600 lb (about 1.8 tons to haul). Water ≈ 45 × 0.7 = 31.5 gallons, added a little at a time.
10 ft³ with 60-lb bags
Bags = 10 ÷ 0.45 = 22.2 → 23 bags. Dry weight = 23 × 60 = 1,380 lb. Water ≈ 23 × 0.7 = 16.1 gallons. Yield = 23 × 0.45 = 10.35 ft³, a hair over the 10 ft³ target.
How to measure
- Convert your volume to cubic feet first if you estimated in yards — 1 yd³ = 27 ft³.
- Use the waste-adjusted volume (after your 10% allowance), not the raw geometric volume.
- Weigh your transport realistically: 45 eighty-pound bags is 1.8 tons — plan two trips or delivery.
- Check the bag label at the store: high-strength and fast-setting mixes list their own yield, which can differ from 0.60 ft³.
- Buy the extra 5% in the same batch and brand so color and set time stay consistent.
Assumptions & limitations
Planning estimate
- Bag yields (80-lb ≈ 0.60 ft³, 60-lb ≈ 0.45 ft³, 40-lb ≈ 0.30 ft³) are manufacturer rules of thumb for standard pre-mix; specialty mixes publish their own yields.
- Water at ≈ 0.7 gallons per bag is a rule of thumb — the right amount depends on mix design, aggregate moisture and target slump. Never exceed the water limit printed on the bag.
- Assumes whole bags only and no partial-bag mixing; opened bags absorb moisture and should not be stored.
- This is a planning estimate only — not a substitute for code compliance or professional design. Structural mixes must meet specified strengths.
Frequently asked questions
45 bags. A cubic yard is 27 ft³ and each 80-lb bag of standard pre-mix yields about 0.60 ft³, so 27 ÷ 0.60 = 45. For 60-lb bags it is 60 per yard; for 40-lb bags, 90 per yard.
Roughly 0.7 gallons (about 2.8 quarts) per 80-lb bag is a common rule of thumb, but always follow the bag instructions and add water gradually. Too much water weakens concrete — you want a workable mix, not soup.
Per cubic foot of concrete, 80-lb bags are usually the cheapest option. But 60-lb and 40-lb bags are far easier to carry and mix by hand. For a solo DIY pour, the smaller bags can be worth the premium.
You can, but measure carefully — the cement-to-aggregate ratio is fixed at the factory, so splitting a bag proportionally is fine, but eyeballing it changes the strength. Opened bags also go stale quickly from moisture.
Around 1 cubic yard (45 eighty-pound bags). Beyond that, a ready-mix truck is typically cheaper per yard, arrives consistent, and saves hours of mixing labor. Many suppliers also offer short-load or volumetric trucks for 1–3 yards.