Most rooms are rectangles: length × width. Circles use πr². Triangles use ½ × base × height. Add leftover closets or bays in the extra-area field.
Flooring quotes are in square feet; some materials (carpet remnants, fabric) use square yards (divide by 9). Square meters = sq ft × 0.092903.
Measure wall-to-wall, not just the visible rug. For L-shaped rooms, split into two rectangles and add them.
Take that area into the tile calculator for a floor, or into the grass seed calculator for a lawn. Interior walls can go to the drywall calculator.
How this calculation works
Rectangle L×W; circle πr²; triangle ½bh; optional extra sq ft; also sq yd and m².