The standard way that prices are calculated for granite countertops is by square foot. The way to calculate how much square footage you have in your kitchen, for instance, is to multiply the width by the depth of all of the counters. (Sounds easy enough). Don't forget to add for backsplashes if you have them.
Remember this is only part of a kitchen, you need to add all parts together for a rough estimate.
A countertop that is 10 foot 2 inches (122") long by 26” deep (average depth with overhang for granite)122 inches multiplied by 26 inches = 3172 square inches. Divide this number by 144 and you’ll have the total square feet. 3172 divided by 144 = 22. (Sorry, this sounds like we’re back in high school math class.)
After adding up the entire kitchen, multiply this number by $45 (depending on color selection) and you’ll have a very close estimate of the total. In this case 22 square feet times $45 per square foot (depending on color selection). $45 = $990.00. This figure will usually include the granite material, labor to fabricate (cutting, shaping and polishing), as well as installation.
An average kitchen counter is approximately 40 square foot 40 X $45 = $1,800.00
Other factors that may contribute to the cost are:
1) Additional edge finishing such as on a peninsula top, island or raised bar.
2) Additional holes or cutouts.
3) Under-mount sink cutouts.
4) Tear out of existing countertops,
5) Bracket for overhangs
Note: Do not subtract square footage for sinks and cooktops.
Backsplash is calculated in a similar fashion. Take the length times the width divided by 144 and multiply by $40 (starting price per square foot). This will get you close.