Home & Garden Calculators

How much extra paint should I buy?

Allow for the second coat and a small margin for touch-ups and absorption on new or porous surfaces. Coverage figures on the tin assume ideal conditions, and a textured wall can absorb noticeably more, so rounding up one litre is usually cheaper than an unplanned second trip.

Is the "size by floor area" rule enough for air conditioning?

It is a starting point, not the answer. Ceiling height, glazing area, which way the room faces, insulation and occupancy all change the cooling load, sometimes by a large margin. Use the area rule to shortlist a capacity and then adjust for those factors before buying.

Do I need to allow for pattern repeat on wallpaper?

Yes — a large repeat means every strip after the first must be matched, so more of each roll is trimmed away. The calculation should divide usable roll length by the strip height after adding the repeat, which is why two rooms of identical area can need different roll counts.