Switching from texture() to texelFetch()

Currently I read a 3D texture with the function texture(...) like this:

vec3 value = texture(texture_3D, coord).rgb

What I want to do now is:

vec3 value = texelFetch(texture_3D, coord, 0).xyz

However, I do not know how to convert my coordinate so that it works with texelFetch. My texture is of size 256x256x256

And my current coordinate calculation is as follows:

vec3 min_box = vec3(-0.5);
vec3 max_box = vec3(0.5);

vec3 coord = worldToVolume(world_pos, min_box, max_box)

vec3 worldToVolume(world_pos, min_box, max_box) {
     return (world_pos - min_box) / (max_box - min_box)
}

Any ideas? If you need more information please ask and I will provide it.