ONG charged me $5.888 per dekatherm which is a million btu for August (plus $36.39 in taxes and fees) . I used 0.82 dekatherms. I was charged $50.27 per dekatherm this month. In February, my bill shows I paid $6.05 per dekatherm when I used 18.73 dekatherms at the $3.819 cost of gas rate.
You are paying $2.52 per gallon, that equates into 91,452 btu.
You would need 1,000,000/91,452 = 10.935 gallons of propane for a dekatherm.
I just had 462 gallons of propane delivered at $2.30 a gallon.
A side note - my propane supplier never waits for a call. He services 3 rural counties and nobody has to call. He somehow manages to know when his customers tanks are down about 85% and just arrives, fills, and leaves.