You cannot associate volume and length. However, I'll take it you meant to say decametres. There are 10000 millimetres in a decametre. To get the answer here, you find the inverse of 10000. In other words 1/10000 is 0.0001 decametres.
One US gallon is 0.3785 decaliters.
There are 0.1 decaliters in one liter.
A decaliter is 10 liters, so one tenth.
6.54kL is equal to 654 decaliters.
10 decaliters per hectoliter.
70.73 hectoliters is 707.3 decaliters.
Two decaliters is 20 liters.
0.00085 liters is 0.000085 decaliters.
295mL equates to 0.0295 decaliters.
A decaliter is 10 liters, so one tenth.
792 decaliters is 7920L (there are 10L per decaliter).
One millimeter is 0.000001km