For a healthy adult dog that is moderately active:

The recommended amount to feed is approximately 100g of dry food for every 5kg of bodyweight.
i.e. for a 25kg dog; you ought to be feeding around 500g of food per day, split into two meals.

Note:
This amount is only a suggestion and you may need to feed slightly more if your dog is particularly active. Likewise, if you have an older dog (i.e. 5 years+), or if you have a less active dog, you may find that your dog requires slightly less food, or you should consider opting for a food that is lower in energy (protein and carbohydrates).

For Puppies:

If a puppy is weaning (up to about 6-8 weeks of age), then they will need feeding at more regular intervals- i.e. 5-6 times per day, or 4-5 times per day if they are onto 'crunchy' meals (by about 8 weeks of age).

Below is a rough guide of the amount of dry puppy food to feed based on the puppy's weight:

Up to 1kg            50g
Up to 2 kg           80g    
Up to 5kg            175g
Up to 10kg          200g
Up to 15kg          300g
Up to 20kg          450g
Up to 25kg          500g
Up to 30kg          650g
Up to 40kg          850g
Up to 50kg          850g+    

Note:
You should consider moving onto a Junior/Adult Dog Food when your puppy is between 6- 12 months of age, or when they have achieved their full adult weight.