Here's the ADA's calculator. (The image should take you to their site.)
The ADA gives the relationship between A1C and eAG as: 28.7 x A1C – 46.7 = eAG.
Which works out to:
While I'm at it, here's ACCU-Chek's calculator. (The image should take you to their site.)
ACCU-Chek's caveat is important:
"This tool uses average plasma blood sugar readings — the measure used by most meters available today. It should not be used to predict an A1C and is not a substitute for a clinical test performed by your doctor. It is intended to show the relationship between a healthy A1C and self-monitoring results, and give you an idea of how you can help prevent long-term diabetes complications."