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Estimating paint... how much paint do I need?

From the Resene paint and decorating problem solver

To determine how much paint you need for your project you will need the following information:

  1. Surface area of the surface(s) to be painted (excluding areas where there are windows, doors etc).

  2. Spreading rate of the paint being used.

  3. The number of coats needed.

For example:

  1. To paint the living room walls excluding the ceiling. The walls are 3 metres high, each wall is approx 4 metres in width, and windows and doors make up approx 0.5 of a metre of each wall leaving a paintable surface of 3.5 metres per wall. The surface area to paint is therefore 14 metres (4 walls x 3.5 metres each) x 3 metres high = 42 square metres.

  2. The walls are currently painted and are in good condition. Resene SpaceCote Low Sheen is the selected paint system. The product label and data sheet tells us that it has a theoretical spreading rate of 11 square metres per litre. (You can view product data sheets and labels here to get the spreading rate info for the product you plan to use.)

  3. As the walls are previously painted and in good condition, only two coats of Resene SpaceCote Low Sheen are required.

The amount of paint required is therefore:

Surface area: 42 square metres

Divided by
Spreading rate: 11 square metres per litre

Multiplied by
Number of coats: 2 coats

42/11 x 2 = 7.6 litres

This tells us that 7.6 litres of paint is required to paint two coats onto the living room walls. The best idea would then be to purchase 8 litres giving enough paint to complete the job and sufficient to go back if touch up is required later.

To make calculating your paint requirements even easier, use the calculator below. 

Paint Calculator

To work out how much paint is needed for your interior or exterior project use our paint calculator:

  • If you know the 'Surface area' enter it in the 'Surface area' box below, then 'Spreading rate' and 'Number of coats', then click the 'Calculate' button.

  • To calculate the surface area enter 'Height/length' and 'Width' of area to be painted, click 'Calculate Surface Area' and enter spreading rate and number of coats, click 'Calculate'.

(Surface area / Spreading rate) x Number of coats = the litres of paint required

Calculator - How much paint do I need

If you change data entered into the fields below, ensure you press the calculate buttons again to re-run the equations and get the new answers.
Surface Area(m2):
Spreading rate(m2/L)
No. of coats
Calculated result:
Litres in total

NB: Porous surfaces and shapes (ie corrugated iron) will require more paint.

Roof painting tip

A good rule-of-thumb for calculating the quantity of roof paint required is: your project's footprint area plus about 40% (allows for roof pitch, corrugations, soffit overhang, etc). Trough section roofing can require significantly more. Typically a complete roof paint system requires surface preparation using Resene Roof and Metal Wash, one coat of primer and two coats of topcoat at the recommended coverage rate on the cans.

Quick steps...

To estimate paint litres from house plans

To get a rough idea of how much paint you will approximately need when you only have house plans to work from, use the following calculations…

Look for the statement of area on the house plans – e.g. 186m2

Divide this by

10 = litres of sealer for ceilings
5 = litres of 2 coats for ceilings
4 = litres of sealer for walls
2 = litres of 2 coats for walls
25 = litres of primer for trim/doors/frames
15 = litres of 2 coats for trim/doors/frames

Enter the square area (m2) of house plan below and press "Calculate"

You will need...

litres of sealer for ceilings 
litres of 2 coats for ceilings 
litres of sealer for walls
litres of 2 coats for walls
litres of primer for trim/doors/frames
litres of 2 coats for trim/doors/frames

Disclaimer: This quick estimate works as a general guide for most houses, but extreme designs or colour palettes tailored to each room will need a more careful approach with each room calculated individually.

Download the article as a PDF


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