The Concrete Countertop Mix calculator estimates the materials needed for a solid rectangular concrete countertop with a rectangle sink opening. 
INSTRUCTIONS: Choose units and enter the following:
- (L) Length of Countertop
- (W) Width of Countertop
- (T) Thickness of Countertop
- (sWid) Sink Width
- (sLen) Sink Length
Concrete Countertop Mix (cM): The calculator returns the volume (measure) of materials needed for the countertop. The calculator returns:
- (PC) Weight of Portland Cement (Type 1 or Type 2)
- (AP) Alto-Pozz (pozzolans and mineral admixture)
- (SA) Sand / Aggregate (50/50 mixture)
- (WT) Water
- (FM) Fibermesh Reinforcement (PVA 8mm fibers)
- (WR) Water Reducer (Optimum 380 premium superplasticizer)
- (DF) Defoaming and Densifying additive
The calculator also returns:
- (V) Volume of concrete in countertop
- (W) Weight approximation of countertop
- (A) Surface area of countertop
The Math / Science
The calculator first computes the volume of concrete needed for the countertop with a sink opening. The formula for the volume of concrete in a countertop with an opening for a sink is:
V = T* (L*W - sWid * sLen)
where:
- V = volume of concrete in the countertop
- L = Length of Countertop
- W = Width of Countertop
- T = Thickness of Countertop
- sWid = Sink Width
- sLen = Sink Length
Based on the volume of concrete, the following recipe is used for 1 cubic foot of concrete to compute the volume of materials for the countertop:
- 32 pounds of Portland cement
- 8 pounds of Alto-Pozz
- 90 pounds of 50-50 sand / aggregate mix
- 14.5 pounds of water (1.737 gallons)
- 200 grams of fiber mesh (PVA 8mm fibers)
- 120 ml plasticizer (Optimum 380 premium superplasticizer)
- 30 ml defoaming additive (C-64 defoaming & densifying additive)
Thanks to Everything About Concrete and Mike Day for the recipe above. His site provides valuable additional information and guidance.
