Most online calculators for home remodeling--counters, tiling, roofing, siding--do little more than performing simple area calculations. They are less than helpful because they are marketing come-ons to get you to buy a certain product.
However, there are a few that stand out.
Best Siding Calculator: Mitten
The best thing about Mitten's siding calculator is that it breaks apart and adds up all of the various surfaces for you. Most siding calculators ask for total square footage right off the bat. But this calculator does it for you and includes waste materials and those weird surfaces like gables, soffits, and fascia.
Be warned, though: there is nothing all that sophisticated about this siding calculator. It does not do the work for you because, frankly, calculating out siding is a laborious business. Instead, it forces you (in a good way) to think methodically and in separate categories of surface area.
Downside: no price estimates. Also, it's an overall clunky device: often confusing as to which "Calculate" button to press since the form has several.
It is an acceptable tool and with a little revamping, they could make it even better.
Best Tiling Calculator: Warmly Yours
This tiling calculator allows for a more visual, graphic representation of your tiling layout than you might find with other calculators. So, instead of plugging numbers into forms, you get to do the more natural thing, which is moving walls by dragging them with your cursor.
As with all calculators, this one exists to plug a product. In this case, the product is Warmly Yours, radiant heating that installs below the tile. The product plug isn't too intrusive, and it doesn't come until the very end.
One downside is that the company has not made any improvements to this tool since it was released.
Best Roofing Calculator: New England Metal Roof
You're hard-pressed to find a good online roofing calculator that gives price estimates. Most calculators stop at square footage, afraid to venture into the scary world of price estimates.
But New England Metal Roof's calculator mightily tries to peg a rough dollar estimate for your roofing job, including the tear-out of an old roof. Note: this does not just include metal roofs; it also includes composite, wood/cedar, Spanish tile, and many other times of materials, including metal .
One downside is that this online calculator does not let you input a precise roof pitch. Roof pitch does have a very real determining factor on price. However, most homeowners will not get up on the roof or in the attic to measure pitch, and will just estimate anyway. So this calculator's Flat, Low, Medium, Steep, etc. pitch designations work just fine.
The company seems to be on top of this calculator and they do tend to keep it updated.
Best Countertop Calculator: Corian
It's currently a wasteland out there. At one time, the best counter calculator was from DuPont. With their Corian/Zodiaq (quartz) countertop estimator, not only did they take on the mundane task of calculating square footage, but they factored in things like edge treatment and backsplashes. And they worked in price estimates for installation, too.
All of this past-tense is because DuPont may have pulled this plug on this calculator. There merely say that the calculator is "currently undergoing some technical updates." The only problem is that it has been down for technical reasons for a very long time.