Convert Length UOM

Dear Experts,

I'm looking for a way to have length unit of measurements conversion from Metric to English and vice versa. Belowa are the main tables:

- Depth ( i want to choose between ft or m, data can be in either)                   

- Interval ( I want to choose between ft or m, data can be in either)

- Avg speed ( I want to choose between ft/hr or m/hr, data can be in either)