how to measure floor levelness
Lay a 4- to 6-foot beam level on your floor. Check the bubble in the horizontal tube in the level to ensure it floats between the two vertical lines. If the bubble isnât floating between the lines, adjust the level until the bubble floats between the vertical lines. Measure any gap that appears between the floor and the level. If the gap measures less than 1/8 inch, you can consider that area level for flooring installation. Larger gaps require pouring a self-leveling mortar in the depression to level the flooring surface. Mark these depressions with a felt-tipped marker.