Room Paint Quantity Calculator

How Does the Paint Calculator Work?

This calculator estimates paint quantity using a standard architectural formula. The total paintable wall area is calculated as: 2 × (Length + Width) × Height. This gives the total wall surface area of the four walls. That figure is then multiplied by the number of coats planned. The result is divided by the coverage rate of a typical interior wall paint, which is approximately 90 square feet per litre (or about 350 square feet per gallon) for a standard mid-sheen emulsion.

Note: This calculator does not subtract window and door areas. As a general rule, each standard door (about 20 sq ft) and window (about 12 sq ft) reduces your actual area. Deduct accordingly for more precise estimates, and always purchase 10–15% extra as a buffer for wastage and future touch-ups.

Types of Wall Paint: Which One Should You Choose?

Choosing the right paint type is just as important as getting the quantity right. The major categories for interior walls are:

• Distemper (Whitewash): The most economical option. A water-based mixture with very low washability. Good for budget renovations in dry climates. Tends to flake and peel in humid conditions. Coverage: ~120–140 sq ft per litre.
• Matt/Flat Emulsion: A flat, non-reflective finish that hides surface imperfections well. Ideal for ceilings and low-traffic bedrooms. Less washable than higher-sheen options. Coverage: ~80–100 sq ft per litre.
• Eggshell/Satin Emulsion: A slight sheen that offers better washability than matt. The most popular choice for living rooms, bedrooms, and hallways. Good balance of aesthetics and durability. Coverage: ~80–90 sq ft per litre.
• Semi-Gloss: A noticeable sheen with high washability. Best for kitchens, bathrooms, doors, and trim, where walls are frequently touched or exposed to moisture. Highlights surface imperfections. Coverage: ~70–80 sq ft per litre.
• Exterior Emulsion: Formulated with UV-resistant pigments and weather barriers. Essential for outdoor walls exposed to rain and sunlight. Should not be used for interiors. Coverage varies by brand and texture.

How Many Coats of Paint Do You Need?

The number of coats required depends on the colour change magnitude and the paint type:

• Light over Light (e.g., cream over white): 2 coats is usually sufficient.
• Dark over Light (e.g., deep navy over cream): 2–3 coats. Dark colours tend to have good pigment concentration.
• Light over Dark (e.g., white over dark red): This is the hardest scenario. You may need 3–4 coats, or a dedicated primer coat first. A quality stain-blocking primer can save significant paint and effort.
• New Drywall / First Coat on Bare Wall: Always apply a primer coat first. Bare plaster or drywall is highly absorbent and will consume twice the paint it otherwise would without priming.

Tips for a Professional Paint Finish

• Always use a primer on bare surfaces. Primer seals the surface, prevents paint absorption, and dramatically improves adhesion and colour accuracy.
• Sand between coats. A light sanding with 220-grit sandpaper after the first coat has dried creates a smoother surface for the second coat and eliminates brush marks.
• Paint in the right order: Ceiling first, then walls, then trim and skirting boards. This minimises drip damage to previously painted surfaces.
• Cut in before rolling: Use a brush to "cut in" (paint 2–3 inches along edges, corners, and around fixtures) before using a roller on the main wall surface.