Oven Temperature Conversions - Fan Ovens

I couldn't find any links, though I am sure there are some, to sort this out. So far, I have been following Elynor's advice and adding extra flour to my US baking recipes and that has been working out great - things are rising, at least. The problem is, I never seem to get the temperatures right. We have a fan oven. I convert the temperature in Fahrenheit by dividing in half, minus about ten degrees to get a Celcius temperature. But taking the fan oven into consideration, should I be dividing in half, then subtracting 20 or 30 degrees or more? For example, if a recipe calls for 325 F, should I go with 150 C or even less? Thanks!

I use this site for my conversions, because I don't trust my brain: http://www.bbc.co.uk/food/recipes/converter_index.shtml

Then, I just turn the temp back a touch for my fan oven.

Yes, I convert from F to C (using an app on my iPhone, although I now have some standard one (350/450 etc) memorized) and then subtract 20.  And then pray because even WITH a fan our oven is unbelievably uneven and makes baking exciting. It still seems to cook faster than I think it will--I'm sure that as soon as I get used to it I will appreciate the speed, but right now it makes me paranoid about burning things.

I've always heard that the general rule of thumb is to deduct 20C degrees and 10 minutes from the cooking time when using a fan oven.

I have a cheater conversion chart on the side of my fridge.  I take off 20 C for my fan oven, but usually don't need to alter the cooking time.

I have a cheater conversion chart on the side of my fridge.  I take off 20 C for my fan oven, but usually don't need to alter the cooking time.

Me too... alter the temp, but not the time.

Thanks! I will just try going down 20 degrees from the converted temperature and see what happens.