Comparing surface area with volume
Surface area is the combined area of the outer boundary exposed to the surroundings. Volume is the amount of three-dimensional space contained within the organism or structure.
The surface area to volume ratio (SA:V) compares the exposed area with the volume inside.
When an organism or structure becomes larger, its SA:V ratio becomes smaller because the increase in internal volume outpaces the increase in surface area.
| Cube side length | Surface area | Volume | SA:V |
|---|---|---|---|
| 1 cm | 6 cm² | 1 cm³ | 6:1 |
| 2 cm | 24 cm² | 8 cm³ | 3:1 |
| 3 cm | 54 cm² | 27 cm³ | 2:1 |
The largest cube has the greatest total surface area, yet the amount of surface available for each unit of volume is lowest.