Why does the calculator add 54 % to the finished volume?

Loose dry ingredients contain air voids. The 1.54 multiplier ensures you batch enough bulk material to yield the required compacted concrete volume.

Is the water-to-cement ratio entered by weight or volume?

Enter it by weight. A value of 0.50 means 0.50 lb of water for every pound of cement.

Can I use decimal mix ratios such as 1 : 1.5 : 2.5?

Yes. Any positive decimal or whole number works; the calculator scales the ingredient volumes automatically.

Which material densities does the tool assume?

Cement 2427 lb/yd^3, sand 2589.84 lb/yd^3 and gravel 2679.99 lb/yd^3. Replace these constants in the script if your lab values differ.

Spike's Calculators

Imperial Concrete Slab Mix Calculator

Self-Mix Concrete Slab Calculator. AI generated image

The Imperial Concrete Slab Mix Calculator calculates the quantities of cement, sand, gravel, and water needed to pour a level slab when measurements are in feet, inches, and pounds. Enter the slab's length, width and depth, choose a three-part mix ratio (for example, 1 : 2 : 3) and specify the water-to-cement ratio by weight.

The tool:

converts slab volume from cubic feet to cubic yards
adds a 54 % allowance for the extra space taken by loose, uncompacted ingredients
apportions that dry volume across cement, sand and gravel according to the mix ratio
converts each component to weight using typical bulk densities (cement 2427 lb/yd³, sand 2589.84 lb/yd³, gravel 2679.99 lb/yd³)
calculates batch water from the chosen w/c ratio, then reports it in pounds, US gallons and Imperial gallons
returns the total batch weight so you can verify load limits or order ready-mix

Modelled initially on ACI field-batch charts adopted in North America in the 1940s, this workflow remains standard practice for on-site concrete work. Use the calculator to plan material deliveries, double-check supplier tickets, or fine-tune small-batch mixes.

Self-Mix Calculator - Slab

Mixing Ratios
Cement #
Sand       #
Gravel    #

Cement/Water Ratio
#

Length of Slab
ft

Width of Slab
ft

Depth of Slab
in

Results:

Volume of Concrete Needed
yd³ ft³

Dry Volume (with 1.54 multiplier)
yd³

Volume and Weight of Cement
yd³ lbs

Volume and Weight of Sand
yd³ lbs

Volume and Weight of Gravel
yd³ lbs

Water
US gal
lbs
Imp gal

Total Weight of Mix
lbs

Calculator

enter the cement, sand, and gravel mixing ratios
the cement/water ratio for the mixture
the length of the slab in feet
the width of the slab in feet
the depth of the slab in inches

Results

the volume of the concrete in cubic feet and cubic yards
dry volume of ingredients
the cement volume in cubic yards, the weight in pounds
sand volume in cubic yards and weight in pounds
the gravel volume in cubic yards and weight in pounds
required water in US gallons, pounds, and Imperial gallons
the combined weight of all materials in pounds

Dry Volume:

This calculator helps estimate the materials needed to mix concrete for a slab, making it easy to plan construction projects.

Concrete Slab Mix - Calculation Formulas (Imperial)

$$V_{ft} = L\,W\,\frac{D}{12} \quad [\text{ft}^3]$$ $$V_{yd} = \frac{V_{ft}}{27}$$ $$V_{dry} = 1.54\,V_{yd}$$ $$P = c + s + g$$ $$V_c=\frac{c}{P}V_{dry},\quad V_s=\frac{s}{P}V_{dry},\quad V_g=\frac{g}{P}V_{dry}$$ $$M_c = 2427.199\,V_c,\; M_s = 2589.83999\,V_s,\; M_g = 2679.99975\,V_g$$ $$M_w = \left(\frac{w}{c}\right)M_c$$ $$G_{US} = \frac{M_w}{8.345},\qquad G_{Imp} = 0.832674\,G_{US}$$ $$M_{\text{total}} = M_c + M_s + M_g + M_w$$

Worked example

Slab 12 ft * 10 ft * 4 in, mix 1 : 2 : 3, w/c = 0.60

Item	Result
Finished volume $V_{ft}$	40.0 ft³
Finished volume $V_{yd}$	1.48 yd³
Dry volume $V_{dry}$	2.28 yd³
Cement weight $M_c$	964 lb
Sand weight $M_s$	2 360 lb
Gravel weight $M_g$	3 441 lb
Batch water $M_w$	579 lb (69.4 US gal)
Total batch weight	7 344 lb

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