How Much Concrete for a 10×36 Post Hole? (Bags, Yards, and Cost)

By Mike Shutter

A single 10-inch by 36-inch post hole takes about 0.06 cubic yards (1.64 cubic feet) of concrete — call it three 80-pound bags or four 60-pound bags. For the most common DIY scenario, four 10×36 deck post holes, that’s roughly 0.27 cubic yards with 10% waste, or twelve 80-pound bags. The table below shows three common sizes per hole, before waste:

Hole (diameter × depth)Volume per hole60-lb bags80-lb bagsWeight
8″ × 24″ (fence post)0.70 ft³ (0.026 yd³)22105 lb
10″ × 36″ (deck/pergola)1.64 ft³ (0.061 yd³)43245 lb
12″ × 36″ (deck pier)2.36 ft³ (0.087 yd³)64353 lb

Numbers above assume an empty hole. The calculator subtracts post displacement automatically if you specify a post size. For your exact dimensions and hole count, run the concrete post-hole calculator.

How the math works

Each hole is treated as a right cylinder. Net volume per hole is:

V = π × (d/2)² × h

with diameter d and depth h in matching units. Multiply by the number of holes. If a post sits in the wet concrete, the calculator subtracts the buried cross-section of the post over the hole depth: a 4×4 nominal post displaces a 3.5″ square, a 6×6 displaces a 5.5″ square, and a round steel post displaces its actual diameter.

Bag counts follow each bag’s published yield. Quikrete Concrete Mix #1101 yields 0.45 ft³ per 60-pound bag and 0.60 ft³ per 80-pound bag — counts round up, since concrete doesn’t ship in fractions. The waste factor is applied last, as a multiplier on net volume.

Bagged or ready-mix?

At typical post-hole sizes, bagged wins. Four 10×36 deck holes is twelve 80-pound bags — under half a pallet, no truck minimum, and you can mix one batch per hole so nothing kicks before you’re ready to set. A six-post fence run at 10×42 with waste is twenty-one bags, still bagged territory.

Ready-mix starts making sense around a cubic yard of net concrete — roughly twenty to thirty residential post holes, or any commercial install. Most suppliers won’t deliver less than a yard, and short-load fees on small deliveries erase the per-yard cost advantage. For the rare bagged-isn’t-viable case — a ten-hole 24×60 commercial install is 5.8 cubic yards, or 262 eighty-pound bags — the ready-mix call is obvious. Run your actual hole count through the calculator to see which side of the threshold you’re on.

Frost line, footing depth, and rebar

For most post-hole projects the failure mode is frost heave, not load. The IRC requires footings to extend below the local frost line (Section R403.1.4.1); depths range from negligible along the Gulf Coast to 48 inches or more across the upper Midwest and northern New England. Your local building department publishes the depth for your jurisdiction — start there, not from a national chart.

Deck post footings are also sized by tributary load and soil class under IRC Section R507.3, which sets minimum footing diameters for residential decks. For wood posts in direct contact with concrete or soil, IRC Section R317.1 covers preservative-treatment requirements. Rebar in a single-post footing is rarely required for fence or light deck loads; a column footing carrying meaningful lateral load — a tall pergola, a sign post in wind country — is a separate conversation with a local engineer.

Cost at typical sizes

Concrete cost at post-hole volumes is dominated by retail bag pricing. An 80-pound bag of Quikrete or Sakrete Concrete Mix runs roughly $5–$8 at big-box retail across most US markets in 2025–2026, with metro markets and the Northeast trending higher. The four-hole deck example is twelve bags with waste, so about $60–$96 in concrete. A six-post fence at 10×42 is twenty-one bags, about $105–$168. Add a few dollars per hole for crushed-stone base.

Ready-mix is priced per cubic yard plus fees: $150–$200 per yard has been typical since 2024, with short-load fees of $40–$120 on deliveries under three yards, and additional fees for Saturday or after-hours pours. Below about 1.5 cubic yards of net concrete, bagged is cheaper — and at our typical residential sizes, that’s almost always the case.

Common mistakes

Under-ordering. Augers don’t produce smooth cylinders. Clay sloughs, gravel falls in, and the actual hole takes 5–15% more concrete than the geometry says. The default 10% waste factor covers most of this — don’t zero it out “because the math is exact.”

Setting wood posts directly in concrete. Wet concrete wicks moisture into post end-grain; rot starts at the buried collar and works upward. The trade alternative is a galvanized post base bolted to a concrete footing, with the post above grade. IRC Section R317.1 covers the wood-treatment rules when direct ground contact is unavoidable.

Generic depth rules. “Three feet for a fence post” works in Georgia and fails in Vermont. Use the post-hole calculator with your actual local frost depth, not a national number.

Too much water. The water ratio printed on the bag is a maximum, not a target. Each extra cup drops compressive strength noticeably.

Get exact bag counts, volume, and post-displacement-adjusted numbers for your project with the Concrete Post-Hole Calculator.

References