How to Determine your Paint Requirements

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How to Determine your Paint Requirements

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Project Overview

You can save yourself time and money by pre-determining the volume of paint you require before purchasing. This will ensure you do not run out of paint in the middle of your painting task and limit paint wastage from purchasing too much.

Also, check out our paint calculator to help calculate how much paint you need for your next painting job.


Read the instructions before beginning your project.
Always keep tools and materials away from children. 
Safety glasses should be worn at all times.

Step by Step Instructions

1 Calculating area for a rectangular room
2 Calculating the area of a room of unusual shape
3 Trim
4 Doors
5 Coverage
6 Planning
7 Hints and Tips
  • Step 1. Calculating area for a rectangular room

    For a rectangular room with average sized windows and doors; Measure the length and width. Round off each figure to the nearest half-metre and add them together. Multiply the total by the room height, then double that result. The final figure is the area of your walls in square metres. From this total, subtract 1.5 square metres for each of the windows and 2 square metres for each door. Ceiling area is the length multiplied by the width of the room.
  • Step 2. Calculating the area of a room of unusual shape

    First measure the height and width of each rectangular section to be painted. Multiply these figures to get the area, then add them together for the total area. A stairwell often forms a triangular shape. For the area of the triangle, multiply the lengths of the horizontal and vertical legs and divide by two.
  • Step 3. Trim

    If you plan to paint the trim a different colour, calculate these areas separately.
  • Step 4. Doors

    Allow 2 square metres for each side of a door and 1.5 square metres for a single size window frame. A skirting board area is its height times its length (which is generally the same as the perimeter of the room). When you know the total area you will cover, you have half the information you need to order paint. The rest depends on the covering capacity of your paint and the surface it must coat.
  • Step 5. Coverage

    If your walls are smooth, estimate on covering 8 square metres with a litre of matt or semi-gloss paint. Divide your area figure by that amount to arrive at the number of litres you need for a first coat. If you are using finishing paint on porous, rough or previously unpainted walls, a litre will cover considerably less than that.

    You can count on more coverage for the second coat. Always check the coverage information on the label of the paint can, as different types of paint have different spreading capacities. Five litres of paint is generally ample for a 4m x 5m room with a 3 metre ceiling and smooth, previously painted walls. The ceiling of the 4m x 5m room would take 1.5 litres (if you must buy 2 litres, you can reserve the extra for repairs). Professional painters often allow for one quarter as much trim paint as wall paint. You can make a more accurate and economical purchase if you calculate the trim area as suggested above. How long will it take? Estimating time brings in a new set of variables. In one hour you are likely to cover about 7 square metres of an ordinary surface, or about 5 square metres of bare wood or plaster.

    You will probably be able to paint that 4m x 5m room with one coat in five to six hours. If you apply two coats, you must allow time for the first coat to dry. Allow four hours for water-based paint and overnight for oil-based paint (check the paint can label). You can safely reckon on two or three days to paint a room and clean up afterwards.

  • Step 6. Planning

    Bunnings Warehouse can give you expert advice on colour schemes and what types of paint to use where. We can also save you money by calculating quantities. Tell us the measurements of the areas you want to cover, the types of surfaces and their condition. All this information will make calculations a lot easier.
  • Step 7. Hints and Tips

    • Top quality paints not only give you easier and better coverage but are longer lasting and easier to clean than low grade paints. Budget for the best - it pays in the long run.
    • Mould: Generally occurs on warm, moist surfaces in rooms with poor ventilation such as bathrooms, laundries and sometimes bedrooms. It can be treated with household chlorine bleach, followed by rinsing with clean water. Sometimes this is enough to restore the appearance of the painted surface without repainting. If the conditions remain favourable for mould growth then re infection may occur. The installation of exhaust fans and a skylight in these areas is recommended. Further protection can be had by choosing a paint that incorporates mould deterrent. This helps prevent new mould spores from developing but it will not kill existing mould. Ask our experienced advisors at your nearest Bunnings store for advice.
    • Mould/mildew/moss or lichen: Often occurs on surfaces that remain damp for extended periods. These are best treated with a bleach solution, such as household bleach. Rinse off the residue and repaint with a paint containing a mould deterrent to prevent future re infection of the surface.
    • Paint spills/drips: Spills on carpets or upholstery should be covered with polythene sheet or Glad wrap to prevent them drying out. Seek help from a professional carpet cleaner immediately. Paint drips and splatter on enamelled or varnished surfaces should be wiped up immediately with a cloth wet with water (water-based paint) or turps (oil-based paint). Dried drips can often be removed with lacquer thinner without damaging the surface.
    • Brushes: For trim work i.e. skirting boards and window frames 25-63mm brushes are recommended. For larger areas use 75-100mm brushes. For a satisfactory finish always select quality brushes, rollers and accessories.
    • Rollers: The choice of rollers depends on the surface being painted and the paint being used. For high gloss paints use a short nap roller. For flat, low sheen or semi-gloss paints use a medium nap roller. For rough surfaces use a long nap roller. It is wise to select a roller frame with a threaded handle so it can be used with an extension handle if required. Brushes or shirline applicators are best for painting woodwork. Use a paint aid to keep paint off walls and floor. Do not apply paint too heavily or it will run. 

Please make sure you use all equipment appropriately and safely when following the advice in these D.I.Y. videos. You need to be familiar with how to use equipment safely and follow the instructions which came with the equipment. If you are unsure, you may feel it is safest to consult an expert, such as the manufacturer or an expert Bunnings team member.

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