Why coverage on the can is optimistic
The spreading rate printed on the can, around 11 to 12 square metres per litre for a typical NZ wall paint, is a theoretical figure. It is measured on a dead-flat, sealed test panel at an ideal film thickness in a lab. Your walls are not that panel.
In the real world the paint goes less far. A rough or textured surface has more area than its flat measurement suggests. Bare or porous surfaces drink the first coat. Some paint stays on the roller, some on the tray, some gets over-applied cutting in around trim. All of it pulls your real coverage below the printed number. The fix is simple: treat the can figure as a best case, and round your litres up rather than down. Running out with one wall to go means a second trip and a colour that might not quite match.
Prep beats paint every time
The paint is the easy part. The finish you actually see comes from what happens before the topcoat. Fill the holes, sand the flaky bits back, wash off the grease and dust, and seal anything new or bare. A new plasterboard wall needs a sealer before it will take a topcoat evenly, otherwise the board sucks the paint in and the finish goes patchy.
That is why this tool has a new-or-porous toggle. Tick it and it adds a sealer coat to your paint total, because a fresh surface genuinely needs one before the two topcoats go on. Skipping the seal to save a can is the false economy that shows up as a blotchy wall in the afternoon light.
Sheen: pick it by the room
Sheen is not just a look, it is how the paint behaves. The rough rule for a NZ home:
- Low sheen or matte for living rooms, bedrooms and ceilings. It hides wall imperfections and reads soft.
- Semi-gloss or satin for kitchens, bathrooms and hallways. It wipes clean and shrugs off moisture and scuffs.
- Gloss or semi-gloss for doors, skirting and trim, where you want a hard, wipeable edge.
Higher sheen shows every bump, so the shinier the paint, the better your prep needs to be. That is another reason bathrooms and kitchens are worth the extra sanding.
How pros quote a paint job
A painter does not quote you the paint, they quote you the labour, and the paint is a small line at the bottom. The bulk of a professional quote is time: masking, prep, cutting in, two coats, and the tidy-up. That is why two identical-looking rooms can quote wildly differently, one has good walls and the other has forty holes to fill.
If you are pricing your own time against a quote, the honest DIY-versus-pro line is this: doing it yourself saves you the labour, not the paint, and the labour is most of the cost. A pro also owns the finish, so if a wall goes wrong they fix it. Working out what your own hour is worth is the same maths a tradie does. Our trade hourly rate calculator runs those numbers if you want to compare properly.