Eight-foot bays. Hole diameter is 3 × the actual 3.5 in post (10.5 in). Depth is one-third of the post. Bag count uses Quikrete Concrete Mix 1101 at 0.60 cubic feet, mixed per hole and rounded up — the same 80 lb SKU as the slab tool ($5.98). Fast-Setting 1004-50 is quoted below, not used as the engine.
Basket 2026-08-27
Run and posts
Buy this month
6 panels
7 posts · 21 bags of 80 lb · 10.5 in holes × 2.667 ft
$202.44
Bays
6 × 8 ft
Cu ft / hole
1.604
Bags / hole (1101)
3
Bags $
$125.58
Posts $
$76.86
Panels $
null
Engine is Quikrete Concrete Mix 1101 at 0.60 cu ft, mixed per hole. Fast-Setting 1004-50 (Nov 2025) is a quote on the method page, not this bag count.
What calculator.net does not show
A 4×4 is 3.5 in actual. Three times that is 10.5 in, not a round 12 in. Quikrete Fast-Setting Concrete Mix 1004-50 (revised November 2025) tells you to dig about three times the post diameter and bury one-third of the overall post height. That geometry is what this page uses. The bag math is still 1101 / 0.60 cu ft, because that is the 80 lb mix in the dated basket. Fast-Setting 50 lb yield is about 0.375 cu ft; two 50 lb bags set a 3 in square post in a 9 in × 30 in hole. That sentence is a quote. It is not this calculator.
Worked US example: 48 ft run, 8 ft posts
Bays / panels = 48 ÷ 8 = 6
Posts = 6 + 1 = 7
Hole = 3 × 3.5 in = 10.5 in diameter
Depth = 8 ÷ 3 = 2.667 ft
Cu ft / hole = π × (10.5/24)² × 2.667 = 1.604 cu ft
Bags / hole = 1.604 ÷ 0.60 = 2.673 → buy 3 (1101, round up per hole)
Bags total = 7 × 3 = 21
Bags @ $5.98 = 21 × $5.98 = $125.58
Posts @ $10.98 = 7 × $10.98 = $76.86
Panels = $ null
Optional 10% is the same labelled convention as the slab calculator. Panel dollars stay empty until you type a local style.
Citations
The Quikrete Companies. QUIKRETE Concrete Mix product data (No. 1101). Accessed 2026-08-27. https://www.quikrete.com/pdfs/data_sheet-concrete%20mix%201101.pdf — Revised October 2022. An 80 lb bag yields approximately 0.60 ft³; a 60 lb bag yields approximately 0.45 ft³. The published calculator method is divide volume by yield and round up to the next bag — no waste percentage.
The Quikrete Companies. QUIKRETE Fast-Setting Concrete Mix product data (No. 1004-50). Accessed 2026-08-27. https://www.quikrete.com/pdfs/data_sheet-fast%20setting%20concrete%20mix%201004-50.pdf — Revised November 2025. Quote only: dig the post hole about 3 times the diameter of the post; hole depth should be 1/3 the overall post height. 50 lb bag yields approximately 0.375 cu ft. Two 50 lb bags set a 3 in square post in a 9 in diameter hole 30 in deep. The fence calculator’s bag engine is Concrete Mix 1101 at 0.60 cu ft, not this sheet.
These calculators estimate material takeoff for planning. They are not engineering, structural, or code advice. Confirm spans, mixes, fastener schedules, and permits with a licensed professional and the manufacturer’s current data sheet. Local shelf prices and tax are not this index.