Why Most Buyers Overbuy (or Underbuy) Paint
Walk into any hardware store in Indonesia and you'll find buckets of leftover paint stacked in corners — remnants of someone's miscalculation. Getting the quantity wrong costs money in both directions: buying too much wastes budget, buying too little forces a mid-project run for a color that may not match perfectly after mixing. This guide gives you the formula to get it right the first time.
Step 1: Calculate Your Paintable Surface Area
The net paintable area is not the same as your floor area. You need to measure wall surfaces specifically.
Formula: Total wall area = (perimeter of room × ceiling height) − area of all doors and windows
For a standard Indonesian room of 3m × 4m with 3m ceiling height:
- Perimeter = (3 + 4) × 2 = 14 meters
- Wall area = 14 × 3 = 42 sqm
- Subtract a standard door (0.9 × 2.1 = 1.89 sqm) and two windows (each 1.2 × 1.0 = 1.2 sqm each)
- Net wall area = 42 − 1.89 − 2.4 = 37.71 sqm
If you're also painting the ceiling, add the floor area (3 × 4 = 12 sqm) to your total.
Step 2: Understand Paint Coverage
Indonesian paint products typically state coverage on the label in sqm per liter for a single coat. Common benchmarks:
- Interior emulsion paint (e.g., Dulux Ambiance, Mowilex Emulsion): 10–12 sqm per liter per coat
- Budget interior paint (e.g., Catylac, Avian): 8–10 sqm per liter per coat
- Exterior weatherproof paint (e.g., Dulux Weathershield, Mowilex Weathercoat): 8–10 sqm per liter per coat
- Primer/sealer: 10–14 sqm per liter per coat
Always plan for at least 2 coats for uniform color. Darker and more saturated colors often require 3 coats to hide the primer.
Step 3: Calculate Total Liters Needed
Using our example room (37.71 sqm wall area, 12 sqm ceiling = 49.71 sqm total):
- With 2 coats: total area to cover = 49.71 × 2 = 99.42 sqm
- At 11 sqm/liter coverage: 99.42 ÷ 11 = 9.04 liters
- Add 10% contingency: 9.04 × 1.1 = 9.94 liters → buy 10 liters
For a full house with 4 rooms, 2 bathrooms, a living room, and exterior walls, expect to use 30–50 liters total depending on house size and number of coats.
Step 4: Primer — Don't Skip It
In new construction or after replastering, primer is mandatory. Unpainted concrete and plaster absorb paint unevenly, causing the final coat to look patchy. A good alkali-resistant primer also prevents efflorescence — the white chalky salt deposits common on exterior walls in humid climates like Bogor and the surrounding area.
Calculate primer separately using the same formula. One coat of primer on your total surface area is usually sufficient.
Step 5: Choosing the Right Finish
Sheen level affects both aesthetics and durability:
- Flat/Matt: Good for ceilings and bedrooms where you want minimal light reflection. Harder to clean; shows marks more.
- Eggshell/Satin: The most popular all-purpose interior finish. Slightly washable, good for living rooms and hallways.
- Semi-gloss: Ideal for kitchens, bathrooms, and wood trim. Resists moisture and is easy to wipe down.
- Gloss: Highly durable, used mainly on doors, window frames, and railings. Very reflective — shows imperfections clearly.
Step 6: Exterior Paint Considerations
In West Java's wet season (October–March), exterior walls absorb moisture aggressively. Choose a paint explicitly rated for tropical climate, with anti-fungal and anti-algae additives. Mowilex and Dulux both produce Indonesia-specific exterior formulas designed for high humidity and UV exposure at the equator.
Exterior paint should be applied only when the wall is fully dry. Wait at least 28 days after plastering before applying any paint system on new exterior walls.
Practical Buying Tips
- Buy all cans for the same color in the same batch (same production code printed on the lid) to avoid color inconsistency between batches.
- For custom mixed colors, buy enough for the entire project plus 10% extra — re-mixing the exact same shade later is nearly impossible.
- Store leftover paint in airtight sealed cans, upside down, in a cool location. Properly stored paint can last 2–3 years for touch-ups.