You can always take a small drill bit and take a stab at it.
How to find hardwood floor joist.
At that point drill a hole where the shoe mold was.
Turn the stud finder on place it on the floor and move it.
The floor might just be nailed to the subfloor there.
The floor joist spacing is the distance between the centers of any two installed joists.
Pull back the corner of the carpet padding with the pliers.
If not you can fill the hole with a speck of putty.
You ll feel the joist if you hit it.
A number of test hole locations are within the photo but they are not visible.
Tear off a small piece of masking tape and place it on the hardwood floor to identify the joist.
Look closely at the carpet near the yellow tape measure.
For 4 inch thick exterior walls measure approximately 12 inches from the exterior wall perpendicular to the run of the hardwood floor.
Look at the subfloor and find a row of nails which are attached to a joist.
Get some wood filling paste to fill in the holes.
Those kind of screws were originally designed to re attach a single board in a place where it had popped loose on a floor made of nailed down individual boards especially squeaky stair treads.
The nails tell you where the first joist is and which.
Sometimes you can get a good idea just by walking on the floor and concentrating on identifying the location of the squeaks.
Looking at this table you will see there is a choice in the size of floor joist 2 x 6 2 x 8 2 x 10 or 2 x 12 and there is a choice in the joist spacing 12 16 or 14.
My floors were pretty wack and although squeek no more did not fully solve the issue the product made a noticeable positive difference in the end.
You can guesstimate where the joist is shoot a screw on either side go underneath and measure where the joist is between the screws go back up and use the measurement to hit it.
That should be about where the first free joist is for 6 inch exterior walls measure 10 inches.
The joists in this part of the house run at a right angle to the yellow measure tape which is consistent with the direction they run in the closet on the other side of the house.
You ll have to drill small holes to find your first joist but you should be able to measure out 16 inches and go from there.