Sidewalks: 4", patios: 4", shed pads: 4-6"
10% is standard for small pours
Concrete Bag Estimate
Bags Needed
10 bags
80 lb bags at $70 estimated (5.87 cu ft with waste)
Tip: For projects needing more than 30-40 bags, ready-mix delivery is usually more cost-effective and easier to work with. A typical ready-mix minimum is 1 cubic yard (~45 bags of 80 lb).
12,800+ estimates calculated this month
Last updated: 2026-02-20
Quick Answer
To figure out how many bags of concrete you need, calculate the volume in cubic feet (Length x Width x Thickness/12), add 10% for waste, then divide by the yield per bag: 0.60 cu ft for an 80 lb bag, 0.45 cu ft for 60 lb, or 0.30 cu ft for 40 lb. One cubic yard takes about 45 bags of 80 lb mix.
Need to estimate a full concrete pour with ready-mix pricing? Use the concrete calculator for cubic yards and delivered cost. For jobs under 1 cubic yard, bags are the way to go. Try EstimationPro free to build a complete concrete estimate with materials, labor, and follow-up built in.
Inputs you'll need
- Project type: slab, post holes, footing, or a known volume
- Dimensions in feet (length, width) and inches (thickness or depth)
- For post holes: diameter, depth, and number of holes
- Bag size preference: 40 lb, 60 lb, or 80 lb
Bags per cubic yard by size
| Bag Size | Yield per Bag | Bags per Cubic Yard | Cost per Yard (bags) |
|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 bags | $270 - $540 |
| 60 lb | 0.45 cu ft | 60 bags | $240 - $480 |
| 80 lb | 0.60 cu ft | 45 bags | $225 - $450 |
| Ready-mix (delivered) | 27 cu ft | 1 yard | $110 - $200 |
Common projects: bags needed
| Project | Dimensions | 80 lb Bags | Approx. Cost |
|---|---|---|---|
| Mailbox post | 8" hole, 24" deep | 1-2 bags | $5 - $20 |
| Fence post (each) | 10" hole, 24" deep | 2 bags | $10 - $20 |
| Small pad | 3x3 ft, 4" thick | 6 bags | $30 - $60 |
| Sidewalk section | 4x20 ft, 4" thick | 25 bags | $125 - $250 |
| Shed pad | 8x10 ft, 4" thick | 49 bags | $245 - $490 |
| Deck post footings (6) | 12" hole, 36" deep, 6 holes | 18 bags | $90 - $180 |
Worked examples
Example A (shed pad, 6x8 ft, 4 inches thick):
- Volume = 6 x 8 x (4/12) = 16 cu ft
- With 10% waste = 16 x 1.10 = 17.6 cu ft
- 80 lb bags = 17.6 / 0.60 = 29.3, round up = 30 bags
- Cost at $7/bag typical = $210
Example B (8 fence post holes, 10" diameter, 30" deep):
- Volume per hole = 3.14 x (5/12)² x (30/12) = 1.36 cu ft
- Total for 8 holes = 1.36 x 8 = 10.91 cu ft
- With 10% waste = 12.0 cu ft
- 80 lb bags = 12.0 / 0.60 = 20, exactly 20 bags
- Cost at $7/bag typical = $140
For larger concrete projects, use the concrete calculator to estimate cubic yards and ready-mix cost. Need to figure out your footing size first? The concrete footing calculator handles continuous and pad footings.
Pro tips from the field
- Buy 2-3 extra bags. You will always use more than the math says. Uneven subgrade, form bulge, and spillage eat up material fast. Extra bags are cheap insurance.
- Mix in batches. Do not dump 10 bags into a wheelbarrow at once. Mix 1-2 bags at a time for a consistent result. Use a hoe to turn the mix, not a shovel.
- Keep bags dry until use. Moisture ruins bagged concrete. Store bags off the ground on a pallet and cover with a tarp. A bag that gets wet and hardens is garbage.
- Time your pour. Avoid pouring in direct midday sun or when temperatures are below 40°F. Early morning or late afternoon gives you the best working conditions.
- Wet the hole or form first. A dry form or dry soil will pull water out of your concrete before it cures properly. Dampen the surface first, then pour.
Common mistakes to avoid
- Adding too much water. The most common mistake. Soupy concrete is easy to pour but much weaker when cured. Follow the bag instructions for water ratio and add slowly.
- Not accounting for waste. Calculated volume is never exactly what you need. Always add 10% for spillage, uneven forms, and imperfect subgrade.
- Mixing too much at once. Concrete starts setting in 15-20 minutes. If you mix more than you can pour and finish in that window, you will waste bags.
- Skipping the subgrade prep. Concrete poured on loose soil, organic material, or standing water will crack and settle. Compact the base and remove any soft spots before forming up.
Building a full project estimate with concrete, labor, and materials? Try EstimationPro free - it builds the estimate, sends the proposal, and follows up with the homeowner automatically so you win more of the bids you already send.
Concrete Bag Guide & Pricing
Bag yields, prices per size, mixing tips, and when to switch to ready-mix delivery.
How Many Bags of Concrete Do I Need?
Divide your total cubic feet of concrete by the yield per bag to get the number of bags needed. A standard 80 lb bag yields 0.60 cu ft, a 60 lb bag yields 0.45 cu ft, and a 40 lb bag yields 0.30 cu ft.
- 80 lb bag: 0.60 cu ft per bag (45 bags per cubic yard)
- 60 lb bag: 0.45 cu ft per bag (60 bags per cubic yard)
- 40 lb bag: 0.30 cu ft per bag (90 bags per cubic yard)
Always add 10% extra for waste, spillage, and uneven forms. Round up to the next whole bag since partial bags are not practical on the jobsite.
Key Takeaways
- 80 lb bag: 0.60 cu ft (45 bags/cy)
- 60 lb bag: 0.45 cu ft (60 bags/cy)
- Add 10% waste factor to your total
Concrete Bag Prices in 2026
Pre-mixed concrete bags cost $3-$10 each depending on bag size and brand. Quikrete and SAKRETE are the most common brands at home centers.
- 40 lb bag: $3-$6 each (best for small repairs)
- 60 lb bag: $4-$8 each (good balance of weight and value)
- 80 lb bag: $5-$10 each (best value per cubic foot)
The 80 lb bag is the most cost-effective per cubic foot, but weighs enough that lifting and mixing becomes serious physical work after 20+ bags. For larger pours, the 60 lb bag is easier on your back and mixes faster.
Key Takeaways
- 80 lb bag: $5-$10 (best value/cu ft)
- 60 lb bag: $4-$8 (easier to handle)
- 40 lb bag: $3-$6 (small repairs)
When to Use Bags vs. Ready-Mix Delivery
Bags make sense for projects under 1 cubic yard (about 45 bags of 80 lb). Above that, ready-mix delivery is faster, cheaper, and produces a more consistent pour.
- Use bags for: Post holes, small pads under 4x4 ft, fence posts, mailbox posts, small repairs, setting anchors
- Use ready-mix for: Driveways, sidewalks, slabs over 4x4 ft, garage floors, foundations
- Break-even point: Around 30-40 bags, ready-mix starts winning on cost and labor time
- Ready-mix minimum: Most plants require 1 cubic yard minimum. Short-load fees ($50-$100 per yard under minimum) apply for partial loads.
Key Takeaways
- Bags: best for < 1 cubic yard
- Ready-mix wins above 30-40 bags
- Short-load fee: $50-$100/yd under minimum
How to Mix Concrete Bags Properly
Add water gradually and mix until the consistency is like thick peanut butter. Too much water weakens the final product. Most 80 lb bags need about 3 quarts of water.
- Mixing methods: Wheelbarrow + hoe (1-5 bags), portable mixer (5-20 bags), mixer rental for larger jobs
- Water ratio: 80 lb bag needs ~3 quarts, 60 lb needs ~2.25 quarts, 40 lb needs ~1.5 quarts
- Working time: About 15-20 minutes per batch before concrete starts to set
- Production rate: One person can realistically mix and pour 15-25 bags per hour with a wheelbarrow
Key Takeaways
- 80 lb bag: ~3 quarts water
- Working time: 15-20 minutes per batch
- Production: 15-25 bags/hour per person
How to Use This Calculator
Select your project type
Choose slab/pad, post holes, footing/strip, or enter a custom volume. Each type uses a different formula to calculate the concrete volume you need.
Enter your dimensions
For slabs, enter length, width, and thickness in inches. For post holes, enter hole diameter, depth, and how many holes. For footings, enter length, width, and depth.
Choose your bag size
Pick 40 lb, 60 lb, or 80 lb bags. The 80 lb bag gives you the best value per cubic foot. The 60 lb bag is easier to handle for longer pours.
Review bags needed and cost
See the total bags needed (with 10% waste included), total weight, and estimated cost. If you need more than 40 bags, consider ready-mix delivery instead.
Concrete Bag Formulas
Slab Volume = Length x Width x (Thickness / 12)
Post Hole Volume = π x (Diameter / 24)² x (Depth / 12) x Holes
Bags Needed = Volume x (1 + Waste%) / Yield per BagWhere:
- Length, Width
- = Area dimensions in feet
- Thickness / Depth
- = Concrete depth in inches (divided by 12 to convert to feet)
- Diameter
- = Post hole diameter in inches (divided by 24 for radius in feet)
- Yield per Bag
- = 80 lb = 0.60 cu ft, 60 lb = 0.45 cu ft, 40 lb = 0.30 cu ft
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Frequently Asked Questions
How many 80 lb bags of concrete make a yard?
You need approximately 45 bags of 80 lb concrete mix to make one cubic yard. Each 80 lb bag yields 0.60 cubic feet, and one cubic yard equals 27 cubic feet. So 27 / 0.60 = 45 bags. At $5-$10 per bag, that is $225-$450 per cubic yard in bags, which is why ready-mix delivery ($110-$200 per yard) is cheaper for larger projects.
How many bags of concrete do I need for a 4x4 slab?
A 4 ft x 4 ft slab at standard 4-inch thickness needs about 10 bags of 80 lb concrete. The math: 4 x 4 x (4/12) = 5.33 cu ft. Add 10% waste = 5.87 cu ft. At 0.60 cu ft per 80 lb bag, that is 5.87 / 0.60 = 9.8, rounded up to 10 bags. Cost: roughly $50-$100 depending on your area.
How many bags of concrete for a fence post hole?
A standard fence post hole (10" diameter, 24" deep) needs 1-2 bags of 80 lb concrete per hole. The volume is about 0.91 cu ft per hole. With waste, that is 1.0 cu ft, which takes 2 bags (0.60 cu ft each). For a 100 ft fence with posts every 8 ft, plan on roughly 26 bags for 13 posts.
Is it cheaper to buy bags or order ready-mix?
Bags are cheaper for small jobs under 1 cubic yard. Ready-mix wins on larger pours. The break-even is around 30-40 bags. Ready-mix concrete costs $110-$200 per cubic yard delivered, while 45 bags of 80 lb mix (1 cubic yard) costs $225-$450 at retail. Ready-mix also saves hours of mixing labor. Most plants charge a short-load fee ($50-$100 per yard) if you order under their minimum (usually 1-3 yards).
How much water do I add to a bag of concrete?
For an 80 lb bag, add approximately 3 quarts (0.75 gallons) of water. A 60 lb bag needs about 2.25 quarts, and a 40 lb bag needs about 1.5 quarts. Start with slightly less water than recommended and add more gradually. The mix should be the consistency of thick peanut butter. Too much water weakens the concrete and increases cracking.
What is the difference between 40, 60, and 80 lb bags?
The difference is yield and handling weight. An 80 lb bag yields 0.60 cu ft and gives you the best value per cubic foot ($5-$10/bag). A 60 lb bag yields 0.45 cu ft ($4-$8/bag) and is easier to lift and mix. A 40 lb bag yields 0.30 cu ft ($3-$6/bag) and works well for small repairs. The concrete itself is the same mix in all three sizes.
How long does bagged concrete take to set?
Standard concrete mix sets in 24-48 hours and reaches full strength in 28 days. Fast-setting concrete (like Quikrete Fast-Setting) sets in 20-40 minutes and can bear weight in 4 hours. Use fast-setting for fence posts and mailbox posts where you need to work the same day. Use standard mix for slabs and footings where you need more working time.
Can I pour concrete bags without mixing?
Yes, for post holes only. The dry-pour method works for fence posts and deck posts: set the post, pour dry concrete mix around it, then soak with water. The concrete absorbs moisture from the ground and sets solid. This method does NOT work for slabs, footings, or any flat pour. For anything structural, always mix the concrete properly before pouring.
How many bags of concrete can one person mix in a day?
A realistic rate is 15-25 bags per hour mixing by hand with a wheelbarrow. In a full day (6-8 productive hours), one person can mix and pour roughly 80-150 bags depending on the project. That is 1.5-2.5 cubic yards. A portable mixer doubles your speed and reduces fatigue. For anything over 40-50 bags, rent a mixer or order ready-mix.
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