In Airtel double data, you have: 3GB for N1000, 7GB for N2000, 18GB for N4000.
HOW TO SUBSCRIBE FOR AIRTEL DOUBLE DATA PLAN
WHAT’S THE VALIDITY PERIOD OF THE DATA?
All data plans are valid for 30 days. However, it is adviceable to subscribe to the data only if you receive the text message. I currently don’t know if you will be eligible for this offer if you didn’t receive the text message from Airtel.
Unlike MTN, you have to buy a new smartphone before you will be eligible for their double data offer.