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Interior design calculators

Paint, flooring, tile and wallpaper quantities with waste, a lighting level estimate, a furniture clearance check, a plan scale converter, and a colour tool with palettes and WCAG contrast.

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Planning aid. These results are planning aids based on the numbers you enter. Verify them against local code (lighting, egress and accessibility rules differ by place) and the manufacturer's data on the tin, roll label or packaging. Order a little extra, and have the qualified person on site confirm anything that matters for safety.

1. Paint

Units

Room length

Room width

Wall height

Doors (count)

Area of one door

Windows (count)

Area of one window

Paint the ceiling too?

Coats

Coverage per litre (typical 10 m²/L; read the tin)

Extra for waste, %

Wall area = 2 × (length + width) × height, minus doors and windows. Coverage depends on the paint, the surface and the method, so use the figure printed on your tin; the defaults shown are only typical (about 10 m² per litre, or about 350 ft² per US gallon). Areas of openings are in the unit squared (m² or ft²).

2. Flooring, tile and quantity with waste

Units

Room length (m)

Room width (m)

Waste allowance, % (about 10 is a typical starting point; more for diagonal or patterned layouts)

Tile width (mm), optional

Tile height (mm), optional

Joint width (mm)

Pack covers (m²), optional

3. Wallpaper

Units

Total wall length to cover (m)

Wall height (m)

Trim allowance per drop (m, top + bottom)

Roll width (m)

Roll length (m)

Pattern repeat (m; 0 for plain or random)

Each drop is cut to the wall height plus the trim allowance, rounded up to a whole number of pattern repeats; whole drops per roll are counted, and drops are ordered as the wall length divided by the roll width, rounded up. Doors and windows are not subtracted (this errs on the side of buying enough). Check the label for roll size, repeat and match type (straight, half-drop), which change the figures; buy rolls from the same batch.

4. Lighting level estimate

Units

Room area (m²)

Room type (typical guidance)

Target level (lux)

Light-loss factor (1 = no losses; real rooms lose some light to walls, shades and ageing; 0.5 to 0.8 is often used)

Lumens per bulb or fitting (from the box)

Lumens needed = area × target level ÷ light-loss factor (in square metres and lux, or square feet and foot-candles). The room-type ranges are typical guidance, rounded, as widely published for homes and offices; they are not a standard. Standards and codes (for example for workplaces, stairs and escape routes) set their own values, which you must check locally. Use more than one level of light: general, task and accent.

5. Furniture clearance checker

Room length (one unit throughout)

Room width (same unit)

Walkway you want, minimum (optional, same unit)

Furniture, one per line: name, width, depth, row. Pieces with the same row number stand side by side along the room length; the row is optional (blank means row 1).

A simple one-dimensional check: the widths in a row are added against the room length, and the deepest piece in each row is subtracted from the room width, leaving the walkway across the room. It does not draw a plan, check door swings or apply any code value. Enter your own minimum.

6. Plan scale converter

Scale

Custom ratio 1 : n (used when "Custom" is selected)

Direction

Length

Length unit

Ratio scales (1:50) mean 1 unit on the drawing is n of the same unit in real life. Architectural scales such as 1/4" = 1'-0" have a ratio of 12 ÷ inches per foot (48 for 1/4"). Printed plans can be shrunk or enlarged by the printer: check against a known dimension or the scale bar.

7. Colour tool

Hex

Pick

R (0 to 255)

G (0 to 255)

B (0 to 255)

H (0 to 360)

S % (0 to 100)

L % (0 to 100)

Contrast ratio (WCAG)

Text colour (hex)

Background colour (hex)

Contrast ratio = (L1 + 0.05) ÷ (L2 + 0.05) using the WCAG 2 relative luminance. WCAG 2 asks for at least 4.5 for normal text and 3 for large text (AA), and 7 and 4.5 for the stricter AAA level. Colours on a screen look different from printed colours and from paint chips: always check a physical sample in the room's own light.