Cookery Question Time!

[SoupDragon]

Help! I have to make a birthday cake for DSs party tomorrow. I've just opened my usual recipe and it calls for 4oz self raising flour. I only have plain. What do I need to add and how much???

Yours
Shambolic Soupdragon of Sanderstead

Baking powder. I'm pretty sure it says on my packet, to make plain into SR flour, you need to add 4 level tsps baking powder to 8 oz flour.
Have used this method many times thanks to dh doing a lot of the shopping and always coming home with the wrong stuff!

Thanks!