Your correct ratio is decided if your sugar readings are well within the range and you do not develop frequent hypoglycaemia
You say you are dividing 7 into carbs that means you are taking 1 unit
for every 7 gm of carbohydrates. So for every 30 points of high sugar you would need 1 unit of Novorapid extra to be taken before the meals.
For example if you have premeal sugar reading of 220 mg/dl and you are planning to eat about 50 gm of carbs in that meal then:
For the 120 high sugar (120 above 100= 220) you would take 4 units of Novorapid extra and for the 50 gm carbs you would take 7 units of Novorapid. So total dose of Novorapid for that meal will be 7+4= 11 units.
If you are following this and have no highs and lows then your this ratio is fine and you do not need to worry but check your HbA1c
every 3 months and keep watch that it is genuinely perfect. I hope you understand. Get back for any related query. Take care.