How to Figure Out How Much Concrete You Need

How to Calculate Yardage for a Slab

The formula is simple: Length × Width × Height = Cubic Feet Then: Cubic Feet ÷ 27 = Cubic Yards

But here’s the catch — you can’t use inches in that formula. Your pour thickness must be converted into decimal feet first.

Why You Need Decimal Feet for Yardage Math

In construction, almost everything is calculated in decimal feet — not inches and not fractions. If you’re pouring a slab, figuring slope, or doing layout, your thickness must be in decimal feet or the math won’t come out right.

This is the no‑nonsense guide, so the goal is simple: understand it, use it, and get accurate yardage every time.

Tenths & Hundredths (Simple Breakdown)

• 1 foot = 10 tenths

• 1 foot = 100 hundredths

• 1 inch = 0.08 feet

• 3 inches = 0.25 feet

• 6 inches = 0.50 feet

• 9 inches = 0.75 feet

• 12 inches = 1.00 foot

These are the only numbers you really need to memorize.

How to Convert Inches to Decimal Feet (Real‑World Method)

Let’s say you’re pouring a 4″ slab.

You don’t add 0.08 four times — that causes rounding errors. Instead, you work off the closest number you already know:

• 3″ = 0.25

• Add 1″ = 0.08

• Total thickness: 0.25 + 0.08 = 0.33 feet

That’s the correct number to use in your yardage formula.

Why We Don’t Stack 0.08 Repeatedly

Stacking 0.08 over and over creates rounding errors. So if you want to find 2″, you don’t do 0.08 × 2.

You do this:

• 3″ = 0.25

• Subtract 1″ = 0.08

• 0.25 − 0.08 = 0.17

This works for every inch — just add or subtract from your 3″, 6″, or 9″ benchmarks.

Why We Divide by 27

Once you have your volume in cubic feet, you divide by 27 to convert it to cubic yards.

Why 27?

• 1 yard = 3 feet

• So: 3 × 3 × 3 = 27 cubic feet

That’s how many cubic feet are in one cubic yard.