| I think in the U.S., a lot of diabetic educators/doctors start people out at 1 unit of insulin for about 15 carbs...then they adjust up or down according to your own personal results.
I don't know if Thailand (is that where you live?) has nutrition labels, but here in U.S. most food grocery items are clearly marked which is a blessing to most of us!
If no nutritional labeling, then purchase a local book on nutrition counts. Breads will vary, some you will just have to guess-ti-mate.
Remember that if you need more insulin to cover your carb intake, then the ratio numbers get lower...1:5 is more insulin than 1:10 or 1:15.
Your weight has a lot to do with your carb metabolism. Everyone is different. Also, expect a slower curve with pasta, rice, potatoes, pizza. Some of those we split our dose, waiting about an hour between total.
You might also get a food scale...the one discussed here lately is a Salter that has a carb counting feature based on weighing foods...you can order from Amazon. | 
