Indoor project calculators

Start with the room. Enter the length, width and wall height once, add the doors and windows, and every indoor calculator works from the same numbers: the wall area for paint and wallpaper, the floor area for flooring and tile, and the perimeter for baseboard and board and batten. An L-shaped room or a room made of several rectangles is entered as it is, not squeezed into one rectangle.

Then choose the material and its package: the coverage printed on the paint can, the area in a box of flooring, the length and width of a wallpaper roll. The calculator adds the waste allowance you set, rounds up to whole packages and shows what will be left over, so the shopping list says exactly how many cans, boxes or rolls to buy. If you already have some, enter them and the list shows only what is still to buy.

Results are estimates from your own measurements and product values. They do not replace the instructions on the product, and they say nothing about structure, wiring, plumbing or permits.

Which indoor calculator to start with

If you are painting and laying a floor in the same room, start with the room refresh planner: you enter the room once and get both lists. If you only need one material, open the matching page. The paint calculator handles walls, ceilings, coats, primer and one can count per color. The flooring calculator works with the box size, the waste allowance, underlay and baseboard. The tile calculator adds spare tiles, trim, adhesive and grout. The wallpaper calculator counts drops per wall and the pattern repeat, the board and batten calculator works out batten spacing and strip lengths, and the curtain fabric calculator turns widths, drops and lining into meters or yards of fabric.

A worked example: one bedroom, paint and floor

Take a room 4.0 m long and 3.5 m wide with 2.4 m walls, one door of 0.8 m × 2.0 m (1.6 m²) and one window of 1.2 m × 1.1 m (1.32 m²). The perimeter is 2 × (4.0 + 3.5) = 15 m, so the gross wall area is 15 × 2.4 = 36 m². Taking off the two openings (1.6 + 1.32 = 2.92 m²) leaves 33.08 m² of wall to paint.

Two coats of a paint with an example coverage of 10 m² per liter need 33.08 × 2 / 10 = 6.616 liters. With a 10% waste allowance that becomes 6.616 × 1.1 = 7.28 liters, which is 2.91 cans of 2.5 liters, so you buy 3 cans (7.5 liters) and about 0.22 liters are left. The floor is 4.0 × 3.5 = 14 m²; with 10% allowance it is 15.4 m², and with boxes of 2.2 m² that is exactly 7 boxes. The calculators follow these same steps and show each of them.

Mistakes the calculators are built to catch

The coverage printed on a paint can is for one coat, so two coats need twice the paint. Doors and windows are taken off the walls for paint, but doorways are not taken off the floor, because flooring normally runs into them. Packages are always rounded up, never down, since running short halfway through a wall is the costly outcome. Walls in one color and a ceiling in white are separate materials and are not added together, because leftover white cannot finish the walls. Finally, the starting values in each calculator are editable examples; replace them with the numbers on the label of the product you are actually buying.