Steps to Determining the Amount of Materials you need:
1. Measure the Size of your Surface
Get your tape measure or ruler out and measure the size of the surface that you are planning to mosaic. The area of the base can be calculated using the following formulas:
Rectangle or square area = length x width
Triangle area = 1/2 x width x length
Circle area = 3.142 x radius x radius
2. Use this quick look up guide to work out how many tiles you'll need
Note: No wastage has been factored into this calculation so don't forget to add an allowance for additional tiles. This will be affected by how much cutting you are planning to do and your level of expertise.
3. A rough formula for calculating the amount of tiles yourself
Square base 50 cm's x 20 cm's = 1,000 cm's
2 cm tile surface area = 2 cm's x 2 cm's = 4 cm's square
How many tiles? 1000 / 4 = 250 tiles
4. Estimating irregular shapes
Rather than using complicated mathematical equations to determine the number of tiles for irregular shapes, you can estimate the number of tiles based on visualisation. For instance, visualise your oval shape as a circle or a hexagon as a smaller square to roughtly estimate the number of tiles.
You can also break complicated shapes up into smaller shapes or use this technique to roughly estimate the quantity of each colour.
5. Always buy more tiles (tesserae) materials than you need
It is always advisable to overestimate the amount of tiles or tesserae for the project rather than underestimate.