Find the Centerline – The first thing you need to do is measure your existing countertop and find the centerline of the sink. Your new counter will have to accommodate the existing plumbing unless you plan to move the sink, in which case you’ll need to modify the plumbing as well. All bathroom sinks require 10 inches of space on either side as well.
Measure the Back – You’ll now need to measure the length of the countertop from the back. Start at the left edge and measure to the right. Add in any additional length you want for the new bathroom countertop (measure from the outside edge of the existing counter to the exact point where you want the new counter to end).
Measure the width of the counter – Start from the back of an open end so your measurements aren’t thrown askew by the backsplash. Measure from the back of the wall to the front edge or to where you want the new front edge to be if you’ll be installing a wider countertop than what you already have.
Account for Variances – You’ll need to account for several additional elements in your measurements. For instance, you’ll need to know the dimensions of the backsplash (depth and height at least, the length should be identical to your counter’s length, unless you intend to install a backsplash only behind the sink itself). You’ll also need to account for the front overhang (usually one inch).
Get the Square Footage – The next step in measuring for a new bathroom countertop is to get the square footage of the counter. To do this, all you need to do is multiply the length times the width and then convert inches to feet. For instance, if your counter will be 96 inches by 24 inches, you would follow this: 96 x 24 = 2304 / 12 = 192. You could then estimate the cost of each countertop material for your application (192 square feet).