Hi Claire ,not an easy answer because it depends what was in the meal.If it was heavy on carbs then even a non-diabetic's levels will go up.In a non-diabetic ,however their levels should return to normal within 2 hours of eating.Normal levels for non- diabetics are around the 4.5 -5 mark.
In someone with diabetes it would also depend on what their blood sugar level was before they started eating the meal .