A simple shelf bracket I designed for use in my office at home, according to Fusion360's static load analysis tool this shelf would be able to handle 1000n of static load force (roughtly 210lbs) per bracket if it were made from injection molded ABS, results will vary wildly with 3d printed materials, however ive been able to acheive over 100lbs of load on these with carbon fiber PLA as long as you print them with enough perimeters to make the honeycomb solid.
I would recommend using a minimum of 4 perimeters with an 0.4mm nozzle, and 20% infill. eventually ill do a full deep dive analysis of load ratings based on print settings and materials, but in the meantime they work really well, look great in my opinion, and fit on most printers pretty easily. Space the brackets every 16"-32" or centered on wall studs and drive 2 screws from the top of the board into the brackets to hold the shelf in place.

I did 16" spacing and 1"x12" plank for the shelf in my office.

for updates on future data regarding these shelves check us out on instagram, @vincent.teune

Update 4-2-20

After initial testing the weight limit of these brackets is still undetermined. i printed out a few brackets with 50% grid infill, 3 perimeters (so that the central honeycomb is solid) and printed in SunTop Carbon Fiber PLA, and they withstood 115.8 lbs of static load for 10 minutes without suffering any plastic deformation. ill have to find a bigger bucket to do a destructive test.

Update 1-3-25

Added ISO Schematic for measurements. Primary units are in mm secondary is in imperial.
Added 4" variant of shelf bracket

Creality

Ender 3 Pro

No

No

0.2mm

20%

best results are achieved with 100% infill, and a minimum of 4 perimeters. for most aplications however 2-4 perimters and 20% infill will be sufficient