In the UK, we use a simple rule of thumb for sizing a septic tank, that is the volume of water per day + 2000L. We have a full guide on sizing a septic tank which can provide you with the detailed calculations, however for ease, here is a table to help:
| Number of bedrooms: | Minimum tank size |
| 1-3 bedrooms | 2750 |
| 4 bedrooms | 2900 |
| 5 Bedrooms | 3050 |
| 6 Bedrooms | 3200 |
| 2 x 2 bedrooms | 3200 |
| 2 x 3 bedrooms | 3500 |
| 2 x 4 bedrooms | 3800 |
There is no harm in going slightly larger in size, it will allow slightly better settlement of solids which could lead to less suspended solids getting into your drainage field.
