How Many Bags of Concrete Per Fence Post? Quikrete Guide
"How many bags of concrete per fence post?" is the question every DIY fence project hits before the Home Depot run. Guess low and you are mixing with concrete setting in the first holes while you drive back for more. Guess high and you haul home a half pallet you did not need.
This guide covers the post-hole formula, a quick 4×4 / 6×6 bag chart, frost depth and gravel tips, and a free fence post concrete calculator that subtracts post volume and rounds bags up per hole — the way you actually buy Quikrete.
Know your Quikrete bag count before you dig
Bags per hole, project total, and cost — free, private, works on your phone at the job site.
How to Calculate Concrete for a Fence Post Hole
A post hole is a cylinder with a post stuck in the middle. Concrete only fills what is left after gravel (if any) and the post itself:
Convert inches to feet first. Concrete depth h = hole depth − gravel base. Bag yields commonly used: 80 lb ≈ 0.60 ft³, 60 lb ≈ 0.45 ft³, 50 lb ≈ 0.375 ft³, 40 lb ≈ 0.30 ft³. Confirm the number on your bag label.
Quick Chart: Bags of Quikrete Per Fence Post
Approximate 80 lb bags per hole with ~6″ gravel and 10% waste. Use the calculator for custom sizes.
- 4×4, 10″ × 24″: 1–2 bags of 80 lb
- 4×4, 10″ × 30″: about 2 bags of 80 lb
- 4×4 frost line, 10″ × 36″: 2–3 bags of 80 lb
- 6×6 gate/corner, 12″ × 36″: 3–4 bags of 80 lb
- 2″ metal post, 8″ × 24″: about 1 bag of 80 lb
Know your Quikrete bag count before you dig
Bags per hole, project total, and cost — free, private, works on your phone at the job site.
Worked Example: 12 Privacy Fence Posts
Twelve 4×4 posts, 10″ diameter × 30″ deep, 6″ gravel, 80 lb bags: each hole needs about 2 bags after per-hole rounding → 24 bags for the run (~1,920 lb of dry mix). Pair gravel drainage with our gravel calculator if you are also topping beds or driveways.
Hole Size, Frost Line, and Gravel Base
Field rules that avoid lean posts
- Hole diameter ≈ 3× post width (10–12″ for a 4×4).
- Depth ≈ ⅓ of fence height, and below frost line in cold climates.
- Add 4–6″ gravel under wood posts for drainage, then pour concrete.
- Use actual lumber sizes (4×4 = 3.5″) when subtracting post volume.
Not structural engineering advice. Permanent fences, tall privacy walls, and gate posts may need deeper footings or local permits. Always follow the bag instructions and your jurisdiction's code.
Why Per-Hole Rounding Beats Project Totals
Dividing total cubic feet by bag yield can under-buy. You open whole bags hole by hole. A free post hole concrete calculator that rounds up per hole matches the shopping list you actually need — the same approach built into our Quikrete fence post calculator.
Related DIY Calculators
- Gravel Calculator — yards and tons for driveways and beds
- Cubic Feet Calculator — convert volumes across units
- Board Foot Calculator — lumber for rails, pickets, and frames
Know your Quikrete bag count before you dig
Bags per hole, project total, and cost — free, private, works on your phone at the job site.
Frequently Asked Questions
How many bags of concrete per fence post?
Most 4×4 posts in a 10″ × 24–30″ hole need 1–2 bags of 80 lb Quikrete. Use the calculator for deeper or wider holes.
How much concrete for a 4x4 fence post?
Plan on about 2 bags of 80 lb mix for a 10×30 inch hole with a 6-inch gravel base.
How many 80 lb bags for 20 fence posts?
At 2 bags per hole, buy 40 bags. Round up per hole — do not stretch partial bags across holes.
Do I need gravel under fence post concrete?
4–6 inches of gravel under wood posts improves drainage. Subtract that depth from the concrete fill calculation.
How deep should fence post holes be?
About one-third of fence height, and below frost line in cold climates. Confirm local code.
Fast-setting vs regular concrete for fence posts?
Fast-setting is convenient for posts; regular mix is cheaper for large jobs with longer cure time.
Should I subtract the post from the hole volume?
Yes — use actual lumber sizes (3.5″ for a 4×4) so you do not over-order by 10–25%.