Paint needed (litres) = Total Area (m²) ÷ Coverage (m²/L) × Number of Coats. We subtract door and window areas automatically since you won't paint those. Always add a 10% buffer for wastage, touch-ups, and future repairs.
A 12×12 foot room (3.65 × 3.65 m) with 8-foot (2.4 m) ceilings has roughly 384 square feet (35.7 m²) of wall area. After subtracting one door and two windows, you're looking at about 30 m² of paintable surface. At standard coverage of 12 m²/litre with two coats, you'd need approximately 5 litres — one standard 5L tin. Use the calculator above with your exact measurements for a precise answer.
A single gallon (3.78 litres) of paint typically covers 350–400 square feet (32–37 m²) in one coat. For an average bedroom with two coats, you'll need about 1.5 to 2 gallons. Larger living rooms or rooms with high ceilings will need more. Switch to Imperial mode in the calculator above for results in gallons and square feet.
The paint finish affects both appearance and durability. Flat or matte finishes hide wall imperfections but are harder to clean — best for ceilings and low-traffic rooms. Eggshell and satin finishes offer a subtle sheen with better washability, making them ideal for living rooms and bedrooms. Semi-gloss and gloss finishes are the most durable and easiest to wipe clean, so they're perfect for kitchens, bathrooms, doors and trim. Higher sheen paints tend to cover slightly more area per litre.
Use a primer on bare surfaces — it's cheaper per litre than topcoat paint and gives a better base, often reducing the number of topcoats you need from three to two. Buy all your tins from the same batch to avoid slight colour differences. Tint your primer close to the final colour when painting dark shades. Keep leftover paint sealed tightly for touch-ups later — label the tin with the room name and date so you know what goes where.
Never use interior paint outdoors. Exterior paint is formulated with UV-resistant pigments, flexible binders that expand and contract with temperature, and mildewcides. Interior paint lacks these additives and will crack, fade and peel within months when exposed to weather. Conversely, exterior paint can release stronger fumes and is not always safe for enclosed spaces, so stick to interior paint inside your home.
Measure the total wall area (perimeter of the room x ceiling height), subtract the area of windows and doors, then divide by the paint's coverage rate (typically 10-12 square metres per litre). Add 10% for waste and touch-ups. For two coats, double the amount. This calculator does the maths automatically.
Most standard interior paints cover 10-12 square metres per litre for a single coat. Premium paints and exterior paints may cover slightly more. Rough or textured surfaces absorb more paint and will reduce coverage. Dark colours may need more coats to fully cover lighter base colours.
Primer is recommended when painting over bare plaster or drywall, painting a dark colour with a light colour, painting over stains, or on previously unpainted surfaces. A good primer improves paint adhesion, can reduce the number of top coats needed, and gives a more even finish.
Exterior paints are formulated to withstand UV radiation, rain, temperature swings, and mildew. They contain different binders and additives than interior paints. Interior paints are designed for easy cleaning and low fumes. Never use interior paint outdoors as it will deteriorate quickly.
Properly sealed latex/water-based paint lasts 2-10 years once opened, if the lid is tightly sealed and stored away from heat and freezing temperatures. Oil-based paint lasts 5-15 years. Signs that paint has gone off include a sour smell, lumpy texture, or failure to mix smoothly even after stirring.
A 12x12 foot room with 8-foot ceilings has about 384 square feet of wall area. After subtracting a standard door and two windows, you need roughly 5 litres (1.3 gallons) for two coats at standard coverage. Use a paint calculator to get a precise figure based on your exact room dimensions and the specific paint you are using.
An average bedroom (10x12 feet) needs about 1.5 gallons of paint for two coats on the walls. Larger bedrooms (12x14 feet or more) will need 2 gallons. Always buy slightly more than you calculate — an extra quart gives you paint for future touch-ups and repairs.
Semi-gloss or satin finishes are best for bathrooms. They resist moisture, mildew, and are easy to wipe clean. Avoid flat or matte finishes in bathrooms as they absorb moisture and stain more easily. For the ceiling, a satin finish also works well to resist condensation and steam damage.