Count how many steps your flight of stairs has. Say, 14 steps. Calculate your needed carpet length by substituting these measurements in this formula: length = riser rise × number of steps + tread run × (number of steps - 1) . That is length = 10 inches × 14 + 12 inches × (14 - 1) = 296 inches .

If the 12 foot by 12 foot room in question is a simple square, multiply those two measurements to equal 144. Therefore, you need at least 144 square feet of carpet. We recommend adding 10% to the total—or multiplying 144 by 0.1 to get 14.1 and then adding that to 144 to get 158.4.

Depending on the application, I most often recommend between 40 oz. to 60 oz. as a good to best moderate weight. Spending more for “high end” 75 oz. carpet doesn't necessarily mean you'll get “high end” performance.