When do we use 'a' or 'an' before words starting with 'k'?

When do we use 'a' or 'an' before words starting with 'k'?

We use 'a' before words starting with 'k' when the sound of 'k' is a hard /k/ sound. We use 'an' before words starting with 'k' when the sound of 'k' is a soft /k/ sound.