The price of posting a letter from the UK to Germany varies depending on its weight. For postage weighing up to 20g, one pays 44p whilst that up to 40g costs 64p. For detailed breakdown of pricing, refer to a Royal Mail Leaflet.
1 Additional Answer
The value of the stamps you will need to stick on your mail to Germany will depend on which service you will be using and the size and weight of the item. For additional information on postage charges, visit the Royal Mail website and check out the table indicating the value and purpose for each stamp.