You'll need
0.07 cu yd · 3 bags
Cost
$18–$30
Project details
What are you pouring?
Post hole / sonotube dimensions
Quantity
e.g. 8 fence post holes, 3 footings
How you'll buy it
Leave blank to use estimate
Default estimate: $130–$180/yd. Most suppliers have a 1–3 yard minimum.
Reinforcement & site prep
Labor
Cost breakdown
Showing bag pricing (80 lb bags).
80 lb bags · 3 bags$18 – $30
Total project cost$18 – $30
💡 Comparison: 3 80-lb bags would cost $18 – $30; ready-mix (1.00 yd) would cost $130 – $180.
Shopping list
Everything you need for this pour.
- 80 lb concrete mix bags3
- Sonotube (10" diameter)1
- Concrete mixing tub or wheelbarrow1
- Mason hoe or mixing tool1
- Gloves, eye protection, knee pads1 set
Ready to pour?
Pick up Quikrete or Sakrete bags at Home Depot.
Math breakdown
Step-by-step from your inputs.
Column volume · π × (0.4166666666666667')² × 31.64 cu ft each
With 10% waste factor1.80 cu ft
Cubic yards · cu ft ÷ 270.07 cu yd
Estimated weight (wet)261 lbs
80 lb bags · ÷ 0.6 cu ft per bag3 bags
Pro tips
8-inch diameter hole, 30 inches deep. Standard fence post: 8-inch wide hole (or 3× the post width), depth = 1/3 the above-ground post height OR below frost line, whichever is deeper.
1-2 bags per 4×4 post. Typical 4×4 fence post in an 8-inch × 30-inch hole takes 1 × 80 lb bag of pre-mix. 6×6 deck posts in deeper holes take 2 bags.
Dry-set is fine for fence posts. For fence posts only: pour dry concrete in the hole around the post, then add water. It cures in place. Saves mixing time on big fence jobs. Don't dry-set deck posts though.
Frequently asked questions
How many bags of concrete per fence post?▾
For a standard 4×4 in an 8-inch × 30-inch hole: 1 × 80 lb bag. For 6×6 deck posts in deeper holes: 2 × 80 lb bags. The calculator handles your exact dimensions.
Concrete for 20 fence posts?▾
If each hole is 8-inch × 30-inch and you use 1 bag per post: 20 bags total. Or if going ready-mix: about 0.5 cubic yards (which is under the typical 1-yard minimum, so bags are usually better for fence projects).
How deep should fence post holes be?▾
1/3 the above-ground height OR below frost line, whichever is deeper. For 6-ft fence (2 ft below ground): 24-inch hole in warm climates, 36-48 inches in cold.
Does concrete around posts cause rot?▾
Yes, for untreated wood. Pressure-treated posts handle direct concrete contact, but the section right at the soil line still rots fastest. For longest life: use treated 6×6, set in concrete with a slight crown so water sheds away.
Related calculators
Concrete Slab Calculator
Calculate concrete needed for any slab — patio, garage floor, shed pad. Cubic yards, bags (40/60/80/90 lb), and total project cost.
Concrete Footing Calculator
Calculate concrete for foundation footings, post footings, and deck footings. Cubic yards, bags, rebar requirements, and total cost.
Concrete Steps Calculator
Calculate concrete for entry steps, stoops, and stairways. Bags, cubic yards, and total cost — handles any number of steps and width.
Concrete Wall Calculator
Calculate concrete for foundation walls, retaining walls, and stem walls. Cubic yards, rebar requirements, formwork, and total cost.
Disclaimer. This calculator provides estimates for planning purposes. Actual material quantities and costs may vary based on site conditions, material availability, and local pricing.