Legally, permitted noise levels in an office vary from country to country. In the Netherlands it shouldn’t exceed 45 decibels; in the UK it’s 55 decibels. But when you consider that a quiet classroom full of students produces 40 decibels, those maximum levels are not very high.
Many employers try to offer employees quiet areas with low noise level so they concentrate. Ergonomic products that help include special sound-absorbing partitions or even separate quiet rooms for working on that particularly tricky report or making an important phone call.