I have been asked this question a few times so I did an analysis of twelve types of wood and the sag for slats that are 3′ wide with thicknesses of 1/2″, 5/8″, 3/4″, 7/8″, and 1″ and span 36″. And based on my construction and bed-building experience I would recommend a minimum of 3/4″ for any wood type.
Pease read my article Make Your Bed Slats Stronger in 7 Steps here.
Scot Boyd
Bed slats should be ¾”, ⅞”, or 1” thick for plywood or solid wood for twin and queen-size frames. A 36” slat span of ¾” plywood sags 0.17” (fixed) and 0.69” (floating), hickory sags 0.10” (fixed) and 0.38” (floating). Increasing wood thickness to 1” reduces sag 60%. Twelve wood types average 0.13” and 0.52”.
Feel free to skip down to the tables below to see my analysis. These tables will assist you in determining the type of wood and thickness you need for your bed project.
And I will create another resource based on this research to include costs for each plywood and solid wood option.
And please let me know if you would like another type of wood added to this research and I will update this information.
For a 36” span for twin and queen-size beds
I am grouping twin and queen sizes together because the queen is twice the width of the twin. Most companies construct the queen-size frame with one of two designs:
- With a center support beam running head to foot for the king so the slats are about 36” long, the same as the twin.
- Utilize two twin frames together to make king-size models.
Wood bed slats should be a minimum of 3/4″ thick for any type of wood. Thicker wood is required if the unsupported span is greater than 36”. 1 x 4” lumber (strapping) should not be used unless substantially reinforced with additional bracing and support framing.
SPF (spruce, pine, fir) is the typical softwood lumber you will find at the lumberyard and hardware stores in the USA and Canada. This is a softwood that has little strength, especially when laying flat, like when used as bed slats.
TIPS to reduce sag (make firmer) read this.
The information in the tables below includes wood spanning 36”. This is a typical span for twin and king-size bed frames. Queen size span is about 28″ so the sag will be considerably less. Usually, the twin bed frame is 38” wide, but the slats will sit on the frame so there is about 36” of unsupported span.
Fixed: This means that the slats are fastened on each end of the bed frame, usually with screws. This produces a substantially stronger construction that reduces sag. The slats move towards the center when not fastened, allowing sag.
Think about a piece of string laid straight on a table. Have someone hold each end in place. Then you put a finger on the center of the string and try to pull it down. It won’t move. Ask your helper to stop holding the ends and you can easily move the string. And the ends of the string move closer together.
Read my article Do Bed Slats Need to be Screwed Down here.
Sag: to bend or hang down in the middle especially because of weight or weakness
Source: Britannica
Wood thickness and types calculated sag for 3” wide by 36” span with 30 pounds per foot center load
| Wood | Thickness“ | Sag “Fixed | Sag “Floating |
| Plywood Fir | ½ | 0.58 | 2.33 |
| Plywood Fir | ⅝ | 0.30 | 1.19 |
| Plywood Fir | ¾ | 0.17 | 0.69 |
| Plywood Fir | ⅞ | 0.11 | 0.44 |
| Plywood Fir | 1 | 0.07 | 0.29 |
| OSB | ½ | 0.58 | 2.33 |
| OSB | 5/8 | 0.30 | 1.19 |
| OSB | ¾ | 0.17 | 0.69 |
| OSB | ⅞ | 0.11 | 0.44 |
| OSB | 1 | 0.07 | 0.29 |
| MDF Med | ½ | 2.00 | 8.00 |
| MDF Med | ⅝ | 1.02 | 4.10 |
| MDF Med | ¾ | 0.59 | 2.37 |
| MDF Med | ⅞ | 0.37 | 1.49 |
| MDF Med | 1 | 0.25 | 1.00 |
| Pine Eastern white | ½ | 0.56 | 2.26 |
| Pine Eastern white | ⅝ | 0.29 | 1.16 |
| Pine Eastern white | ¾ | 0.17 | 0.67 |
| Pine Eastern white | ⅞ | 0.11 | 0.42 |
| Pine Eastern white | 1 | 0.07 | 0.28 |
| Fir White | ½ | 0.47 | 1.87 |
| Fir White | ⅝ | 0.24 | 0.96 |
| Fir White | ¾ | 0.14 | 0.55 |
| Fir White | ⅞ | 0.09 | 0.35 |
| Fir White | 1 | 0.06 | 0.23 |
| Birch Yellow | ½ | 0.35 | 1.39 |
| Birch Yellow | ⅝ | 0.18 | 0.71 |
| Birch Yellow | ¾ | 0.10 | 0.41 |
| Birch Yellow | ⅞ | 0.06 | 0.26 |
| Birch Yellow | 1 | 0.04 | 0.17 |
| Oak White | ½ | 0.39 | 1.57 |
| Oak White | ⅝ | 0.20 | 0.81 |
| Oak White | ¾ | 0.12 | 0.47 |
| Oak White | ⅞ | 0.07 | 0.29 |
| Oak White | 1 | 0.05 | 0.20 |
| Maple Red | ½ | 0.43 | 1.71 |
| Maple Red | ⅝ | 0.22 | 0.87 |
| Maple Red | ¾ | 0.13 | 0.51 |
| Maple Red | ⅞ | 0.08 | 0.32 |
| Maple Red | 1 | 0.05 | 0.21 |
| Hickory Shagbark | ½ | 0.32 | 1.30 |
| Hickory Shagbark | ⅝ | 0.17 | 0.66 |
| Hickory Shagbark | ¾ | 0.10 | 0.38 |
| Hickory Shagbark | ⅞ | 0.06 | 0.24 |
| Hickory Shagbark | 1 | 0.04 | 0.16 |
| Spruce Red | ½ | 0.43 | 1.74 |
| Spruce Red | ⅝ | 0.22 | 0.89 |
| Spruce Red | ¾ | 0.13 | 0.52 |
| Spruce Red | ⅞ | 0.08 | 0.32 |
| Spruce Red | 1 | 0.05 | 0.22 |
| Ash White | ½ | 0.40 | 1.64 |
| Ash White | ⅝ | 0.21 | 0.82 |
| Ash White | ¾ | 0.12 | 0.48 |
| Ash White | ⅞ | 0.08 | 0.30 |
| Ash White | 1 | 0.05 | 0.20 |
| Beech American | ½ | 0.41 | 1.63 |
| Beech American | ⅝ | 0.21 | 0.83 |
| Beech American | ¾ | .012 | 0.48 |
| Beech American | ⅞ | 0.08 | 0.30 |
| Beech American | 1 | 0.05 | 0.20 |
| Douglas Fir | ½ | 0.36 | 1.44 |
| Douglas Fir | ⅝ | 0.18 | 0.74 |
| Douglas Fir | ¾ | 0.11 | 0.43 |
| Douglas Fir | ⅞ | 0.07 | 0.27 |
| Douglas Fir | 1 | 0.04 | 0.18 |
Source
Bed slat 3/4” thickness wood strength comparison (Listed strongest to weakest)
| Wood | Fixed | Floating |
| Hickory Shagbark | 0.10 | 0.38 |
| Birch Yellow | 0.10 | 0.41 |
| Douglas Fir | 0.11 | 0.43 |
| Oak White | 0.12 | 0.47 |
| Beech American | .012 | 0.48 |
| Ash White | 0.12 | 0.48 |
| Spruce Red | 0.13 | 0.52 |
| Maple Red | 0.13 | 0.51 |
| Fir White | 0.14 | 0.55 |
| Pine Eastern white | 0.17 | 0.67 |
| Plywood Fir | 0.17 | 0.69 |
| OSB | 0.17 | 0.69 |
| MDF Med | 0.59 | 2.37 |
| Max | .59 | 2.37 |
| Min | 0.10 | .038 |
| Avg | 0.17 | 0.63 |
| Avg (no MDF) | 0.13 | 0.52 |
Bed slat 1” thickness wood strength comparison (Listed strongest to weakest)
| Wood | Fixed | Floating |
| Hickory Shagbark | 0.04 | 0.16 |
| Birch Yellow | 0.04 | 0.17 |
| Douglas Fir | 0.04 | 0.18 |
| Oak White | 0.05 | 0.20 |
| Beech American | 0.05 | 0.20 |
| Ash White | 0.05 | 0.20 |
| Spruce Red | 0.05 | 0.22 |
| Maple Red | 0.05 | 0.21 |
| Fir White | 0.06 | 0.23 |
| Pine Eastern white | 0.07 | 0.28 |
| Plywood Fir | 0.07 | 0.29 |
| OSB | 0.07 | 0.29 |
| MDF Med | 0.25 | 1.00 |
| Max | 0.25 | 1.00 |
| Min | 0.04 | 0.16 |
| Avg | 0.06 | 0.28 |
| Avg (no MDF) | 0.05 | 0.22 |
Very helpful info. Thanks!
For a king bed, using 3″x3/4″ white ash slats fastened at ends, what spacing between slats would you recommend?
Thanks,
Mark
Thank you for your kind words! For a king bed with 3″x3/4″ white ash slats, we recommend a spacing of approximately 2.5 to 3 inches between slats for optimal support. This helps distribute weight evenly and ensures a sturdy foundation for your mattress.