DEV Community: CalcQuarry

How Much Concrete Per Fence Post Hole? Quick Sizing Guide

CalcQuarry — Sat, 17 Oct 2026 12:04:16 +0000

Setting fence posts is one of those jobs where a small sizing mistake multiplies across 20 or 30 holes. Too little concrete and posts lean after the first wet winter; too much and you have bought a dozen extra bags. Here is a quick way to size each hole and estimate the concrete.

Hole diameter: about 3x the post width

A good rule is a hole roughly three times the width of the post. A 4x4 post (actual 3.5 in) needs a hole about 10 to 12 in across. A 6x6 (5.5 in) needs about 16 in. That leaves a collar of concrete around the post thick enough to resist lateral load from wind and gates.

Hole depth: one third of post height, plus gravel

Bury about one third of the post's total length. For a 6 ft fence on an 8 ft post, that means roughly 2 to 2.5 ft in the ground. In frost-prone areas, go below the local frost line. Then dig an extra 6 in and fill it with gravel. The gravel lets water drain away from the end grain of the post and gives you a firm, level footing.

Estimating concrete volume

Concrete volume is the hole volume minus the post volume, measured above the gravel layer:

Hole volume = pi x (radius squared) x depth
Subtract the post cross-section x buried depth
Add about 10% for irregular hole walls

As an example, a 10 in hole, 24 in of concrete depth, and a 4x4 post comes to roughly 0.95 cubic feet of concrete per hole.

Bag yields

Pre-mixed bags yield approximately:

50 lb bag: about 0.375 cubic feet
60 lb bag: about 0.45 cubic feet
80 lb bag: about 0.60 cubic feet

So that example hole takes about two 60 lb bags or just under two 80 lb bags. Multiply by the number of posts and round up.

Skip the arithmetic

If you are pricing a whole fence line with different post sizes, a post hole concrete calculator will give bags per hole and the total for the job in a few seconds.

Final tips

Crown the top of the concrete so water runs away from the post, check plumb on two faces before it sets, and wait at least 24 to 48 hours before hanging rails or gates.

Paver Patio Base Depth: How Much Gravel and Sand You Actually Need

CalcQuarry — Sat, 17 Oct 2026 07:54:47 +0000

Every paver patio that rocks, sinks or grows weeds between the joints has the same root cause: a base that was too thin or poorly compacted. The pavers you see are the easy part. The gravel and sand underneath do the real work, so it pays to get the quantities right before the delivery truck shows up.

How deep should the base be?

Patios and walkways (foot traffic): 4 to 6 inches of compacted crushed-stone base.
Driveways (vehicle traffic): 8 to 12 inches of compacted base.
Bedding layer: about 1 inch of coarse concrete sand screeded on top of the base.

Go toward the deeper end if you have clay soil, poor drainage or a freeze-thaw climate. Crushed stone with fines (often sold as 3/4-inch minus, road base or paver base) locks together far better than round pea gravel.

Don't forget compaction

Loose gravel shrinks when you run a plate compactor over it. Plan on ordering 10 to 15 percent more than the compacted volume you calculate. Compact in 2-inch lifts so the whole depth gets dense, not just the top.

The formula

area (sq ft)  = length x width
volume (cu ft) = area x depth (in) / 12
cubic yards    = cubic feet / 27

Worked example: 12 x 16 ft patio

Gravel base (6 inches):

Area: 12 x 16 = 192 sq ft
Volume: 192 x 0.5 ft = 96 cu ft
Cubic yards: 96 / 27 = about 3.6 cu yd compacted
With a 15% allowance: about 4.1 cu yd to order

Bedding sand (1 inch):

192 x (1/12) = 16 cu ft
16 / 27 = about 0.6 cu yd

Most suppliers sell by the ton, and crushed stone runs roughly 1.4 to 1.5 tons per cubic yard, so this patio needs close to 6 tons of base.

Quick JavaScript check

const yards = (l, w, depthIn, allowance = 0.15) =>
  +((l * w * (depthIn / 12)) / 27 * (1 + allowance)).toFixed(2);

console.log(yards(12, 16, 6)); // 4.09 (base)
console.log(yards(12, 16, 1, 0)); // 0.59 (sand)

Skip the arithmetic

If you would rather plug in dimensions and get base and sand quantities in one step, the free paver base calculator on CalcQuarry handles depth, compaction and both layers. For converting cubic yards into tons for your supplier, use the gravel tonnage tool.

Final tips

Excavate 6 to 12 inches beyond the patio edges so edge restraints sit on base.
Slope the base about 1/8 inch per foot away from the house.
Lay geotextile fabric over soft soil before adding stone.

Get the base right and the pavers on top will stay flat for decades.

Building a Simple Concrete Volume Formula: Cubic Yards from Feet and Inches

CalcQuarry — Sat, 17 Oct 2026 07:41:31 +0000

Every DIY concrete project starts with the same question: how many cubic yards do I order? Ready-mix suppliers sell by the cubic yard, but we measure slabs in feet and inches. Here is a tiny, dependable formula you can drop into any project.

The math

Measure length and width in feet.
Convert the thickness (depth) from inches to feet: inches / 12.
Multiply length x width x depth to get cubic feet.
Divide by 27, because one cubic yard is 3 ft x 3 ft x 3 ft = 27 cubic feet.

cubic yards = (L ft x W ft x (D in / 12)) / 27

A small JavaScript helper

function concreteYards(lengthFt, widthFt, depthIn, waste = 0.1) {
  const depthFt = depthIn / 12;
  const cubicFeet = lengthFt * widthFt * depthFt;
  const yards = cubicFeet / 27;
  return +(yards * (1 + waste)).toFixed(2);
}

console.log(concreteYards(20, 10, 4)); // 2.72

The optional waste factor adds 10% for spillage, uneven subgrade and over-excavation, which is what most contractors recommend.

Worked example

A 20 ft x 10 ft patio slab poured 4 inches thick:

Depth: 4 / 12 = 0.333 ft
Volume: 20 x 10 x 0.333 = 66.7 cubic feet
Yards: 66.7 / 27 = 2.47 cubic yards
With 10% extra: about 2.72 cubic yards, so order 3 yards.

Edge cases worth handling

Mixed units like 10 ft 6 in: convert to 10.5 ft before multiplying.
Round up when ordering, since suppliers usually sell in quarter- or half-yard increments.
For bagged concrete, one 80 lb bag yields roughly 0.6 cubic feet.

If you want to skip the code and just get a number (plus bag counts), try the CalcQuarry concrete calculator. It uses the same formula and also covers gravel, mulch and paver base.