More of less the IKEA supplies are accurate. Though I didn't use a hammer at all for our install.
The Craftsman tape measure I use has the US standard of 16" on center marked out for the studs. Attaching the shelf to the studs is the only way you can get the best strength possible out of the self
Here's the tape measure I used. Small, compact and includes the stud cheater marks. 12' is a little small for big rooms so you might need a larger tape measure.
Here are the screws I used. 2" to go through the 3/4" drywall and far enough into the studs.
Generally this is what you will do. The only issue is that the holes IKEA pre drilled must be for euro houses and not the standard 16" on center spread of wall studs.
These are the different way to attach the shelf to the wall. We are going to focus on attaching the shelf to the studs but you can also add wall anchors to add strength.
Remember, we will be measuring on center. So measure from the middle of the hole and not from the end.
Find your studs and mark your 16" on center lines on the wall. These will be where you attach the mounts. The small mark on the right is the center of the room. The long mark left is the stud.
Line up the mount and use the available holes to line up with the stud marks. Then mark you area where you will drill the new holes.
As you can see the holes are pre-drilled at 12"' and not the 16" we need to attach the shelf to the stud at. Mark at 16". This is where we will drill the new mounting holes.
Get some good drill bits. These are Dewalt pre piloting bits. Use a 1/4". It will be large enough for your screws.
On your center line drill two holes above one another the same way the original holes are done. This will double the strength of the mount and give the shelf less flex and leverage to pull out.
You don't have to be perfect. Here you can see the new holes screwed to hit those studs.
First just screw the furthest left or right point to attach the mount to the wall. Then place the level on top and swing the mount higher or lower to get it level before attaching the opposite end.
Get everything level. Use the horizontal bubble and get it right between the lines as pictured.
Once you have all the screws attached to the studs slip on the shelf. Final touch, the screws to hold the shelf to the mount.
And here's the finished attached shelf.
Repeat for additional shelves.