Add Plywood to Bed Frame: Detailed Guide

I created this guide to help others make their bed frame more sturdy while saving money. And it can be a fun family project and the kids can help chose their design (might help convince them to help… if you want their help that is).

Or save time with this one from Amazon at 48% off.

Add plywood to a bed frame to make it more sturdy using one or two sheets of 3/4″ structural plywood (not OSB or MDF). Install on top of the existing platform foundation and fasten with screws and lock washers.

Scott added thick 7/8″ plywood

Plywood Thickness

The thickness for a bed depends on if it is used on a platform foundation or a box spring.

Plywood thickness should be 3/4″ thick for Full, Queen, King, and California King size box springs.

1/2″ and 5/8″ can be used for Twin, Twin XL.

3/4″ is best on platform foundations. If installing it on a box spring the corners should be rounded and sanded to prevent damage to the upholstery when weight is applied.

For the platform foundation: How the plywood should be for a bed on a platform foundation depends on the type of foundation:

  1. Metal platforms with thin metal mesh or slats require 3/4″ plywood for Full, Queen, King, and California King.

    5/8″ is adequate for Twin, Twin XL, and Three-Quarter sizes, but if you shell out a couple more dollars you will have more flexibility with what you can do with the plywood when it is retired from supporting sleepers.
  2. Metal and wood platforms with wood slats with gaps less than three-inch only require 1/2″ thick. If the gaps between the slats are 6″- 10″ then 5/8″ thick is fine.
  3. Custom lumber bed frame with joists (lumber on edge rather than think slats on their flats) on 12″ on center (gaps 10″+) should be 3/4″ thick. See the chart below for the approximate costs for lumber and fasteners for a custom wood platform foundation in each size.

Add Plywood to a King Bed

This is a great way to save money, especially if you are using an old-style frame that requires a box spring.

If you want to toss that monstrous rigid block into the garbage then follow the directions below. Remember that the king is wider than the other mattress sizes and requires more wood to build the frame (see Table 1 below).

If you are trying to save money and your mattress is still good and the box spring is shot there is a very cheap option. You can try to extend the life of the box spring by adding plywood instead of slats to the top of it. The thickness should be:

  • 1/4” for a slight increase in firmness. It won’t take long for it to bow into a hammock, but you can flip it over each month when you flip your mattress.
  • 1/2” for a good increase in firmness
  • 5/8” provides even more firmness and has much more lasting power so perhaps you only need to flip it every two months.
  • 3/4” for providing a very firm and sturdy foundation.
  • 7/8” is probably overkill.

TIP 1: Round the corners of the plywood and sand them to prevent the corners from digging into the box spring material.

TIP 2: Purchase two plywood and cut them to the width of the bed and then cut them to fit the second piece to fit the foot.

This creates the joint closer to your feet where bodies are lighter.

And don’t try trimming in pieces around the perimeter. If funds are low then just toss one in the center and give it a try. You can always add more later.

Add Plywood to a King Platform Foundation

If you plan to add a plywood base to a king-size bed on a failing or sub-par platform foundation should not be thinner than 3/4”. And it should be fastened to the frame to prevent it from slipping and moving around. Use tie wraps with the nub under the platform to prevent damage.

Bouncing off protruding wood corners might not feel too comfortable when you are just out of the fart sack in the morning.

Other reasons to consider this modification:

  1. you have a foam mattress, which requires the gaps to be no more than three inches. Many of the top-selling platform foundations have thin wire slats only running in one direction.

    These often have gaps much larger than three inches.

    This cheap fix can greatly extend the life of your foam mattress, as long as you don’t use OSB (Oriented Strand Board) which can pick your foam to pieces and your calves and shins too.
  2. If you have a two-sided mattress you may want to protect the bottom side from damage or overuse on thin metal wires.

    Flipping it each month can certainly help, but for about $23 adding plywood is cheap insurance.
  3. If you are the size of Brian Shaw (450-pound strongman) or if you and the significant other are a little “under-exercised” you may want to add some extra lumber.

    Be certain it covers the entire metal frame to help distribute the weight evenly.
  4. It can help distribute weight more evenly if your metal frame is starting to sag in the middle or if the wires are broken or failing.

A king-size bed is going to require two sheets. One sheet can just barely cover a queen with no waste left over. Some hardware stores sell half sheets so if possible buy 1 full 4′ x 8′ sheet and one 4′ x 4′ sheet.

Scott measuring and marking the cut line
Scott measured and marked the cut line on thick plywood

Best Plywood for Under Mattress

The best plywood to use under a mattress is 3/4” 4′ x 8′ with at least a grade of “Good One Side”. The mattress rests on the good side to prevent damage from the indents and imperfections of the not-so-good side.

This is the largest thickness found in most local hardware stores and costs about $23 ($100 since the pandemic!)

thick 7/8" plywood we are using for this project
Thick 7/8″ plywood we are using for this project

1/2” plywood can work for small children on a twin box spring and a 5/8” can work for larger children or a single person weighing about 130 lbs on box springs up to full size.

But for the small difference in price, it is safer to just go for the 3/4” and make your coffee for a couple of days to save the extra money.

Scott cutting the plywood
Scott cutting the plywood (yes, sometimes being left-handed is a hassle)

TIP 3: Ask your local lumber yard if they carry D-grade, lower-grade, or old sun-weathered stock to save money.

TIP 4: King size and California king require two sheets.

One sheet will perfectly cover a queen box spring but you will need to fill in one side with your cut-off pieces.

TIP 5: DO NOT use MDF (medium-density fibreboard) as it is sawdust glued together so it will not hold its shape laying horizontally with weight unevenly distributed.

And if it ever gets wet, or even in a humid room, it can swell to several times its size and weight.

TIP 6: If you purchase plywood that is “Good Both Sides” you can flip it each month when you flip your mattress to counteract any potential sagging.

TIP 7: If you want ventilation between the plywood and mattress but don’t want to reduce its strength by drilling a thousand holes you can purchase a 4′ x 8′ sheet of vinyl fence lattice and lay that on top of the plywood.

DO NOT go cheap and get the pressure-treated wood lattice as the treatment chemicals are harmful to humans.

Plywood Instead of a Box Spring

Installing a sheet of 1/2” plywood over the metal wires provides a smooth surface that distributes the weight evenly, which extends the life of the mattress.

The extra-long life more than pays for the sheet, which costs on average $27.57 for a 4′ x 8′ sheet.

One sheet should cover up to a queen frame, but you will have to use the left-over cut-offs from the first piece to fill in the remaining areas.

Do not use OSB (Oriented Strand Board) as it will pick at the mattress and cause damage. The edges of OSB are very ragged and your shins and calves can be shredded if you rub against it like cheese through a grater.

You will have a little more work and cost if you have an old-school-style bed frame where a box spring sits inside an angle iron.

The same method above works, except that you will need a minimum of 3/4” which costs on average $35.

But first, you need to build a wood frame for the plywood to sit upon.

Your desired bed height determines which lumber you will need to buy. The below table should help you determine your lumber needs. Also, see the tips below the chart for saving money on this project.

* Pine is an option to make the frame stronger by fastening it to the left and right to cover the ends of the boards. It also prevents the frame from falling like dominoes.

Make sure to sand the edges to prevent the scraping of shins and calves. Some hardware stores sell pine boards by the foot, so you can save money by buying pieces six feet long rather than eight feet.

** 2.5” nails and a hammer are an option if you do not have a drill.

*** You will need to buy a paintbrush if you don’t have one at home (or borrow one from a friend).

**** Due to the longer span the four-inch-wide lumber requires more joists.

DIY wood bed with joists
Frame built for wood headboard and footboard. This should have a couple more joists and more support where the joists meet the rails. With 3/4″ plywood on this Full-size is just enough. I would like to see more joists.

TIP 8: MAKE ANOTHER TABLE. You can reduce the cost of the project by substituting 1” x 4” x 8′ strapping and it will look great stained

TIP 9: Substitute any leftover laminate, hardwood, or vinyl flooring to save even more money (no lumber or stain required).

TIP 10: There is another way to save money if you do not have a truck and don’t want to empty your pockets for a $45 delivery charge of only a small load.

This tip will work if you have a hatchback with fold-down back seats or a sedan with fold-down rear seats.

Measure the width of the opening from your trunk to your interior. Even small cars can handle lumber that is five feet long by sliding it through the trunk and onto the dash.

Measure from the back of the truck to on top of your dash.

Bring rags or towels to place between the dash and the lumber. If your car cannot handle the length of lumber that you need you can let some lumber hang out the back of the trunk and use a bungee cord to hold the trunk closed.

Use a rag or towel between the car and the lumber and make sure to use a red flag available for free from the hardware store (they will staple it to the lumber for you).

“Ahhh”, you say, “what about the plywood dumb dumb”.

For this trick, you will need the lumber yard to cut the ply into two or three lengths so you end up with two or three pieces eight feet long.

The width of the depends on the opening between your trunk and interior (hatchbacks should be able to easily handle it when cut in two pieces).

You aren’t building a piano and nobody will ever see the extra cuts. And it will work just fine too.

Oh, but you will have to put the front passenger seatback as far down into the back seat as possible.

And you may have to push the driver seat up as far as it will go with your knees wrapped around the steering wheel (unlikely, but possible)

TIP 11: If you are ok with a twin bed close to the floor you can simply purchase 1” x 4” x 8′ strapping and cut to length and place it in the frame rails.

Do not leave a space between the slats more than three inches as this is the recommended maximum gap for most mattresses.

This project only costs $20 for ten pieces of 4” lumber (strapping in carpenter lingo).

TIP 12: Sink your fasteners, screws, or nails, below the surface of the plywood or they will pick the upholstery to shreds.

TIP 13: If you do the above method to transport lumber make sure the wood is not pushed up against the windshield.

I loaded up a Jetta one morning and the lumber just BARELY fit.

Perhaps it didn’t fit by about 1/4” because when I closed the trunk it pushed the lumber slightly forward and cracked the windshield all the way across!

TIP 14: My father did this exact build many years ago and he did not cover the sides with any wood and nobody has ever noticed.

And it performs perfectly so this is a much quicker and cheaper option if you don’t want to show off your furniture-making skills.

NOTE: If you chose this method there is an important step that you must take.

For 6” high lumber, you must add two lengths of 1” x 4” x 8′ cut to length and fastened to the bottom of the frame near the rails on each side.

This will support the bottom of your joints so they won’t want to fold over like dominoes.

Mattress on Plywood

Yes, it is ok to put a mattress on plywood under the correct circumstances. For example, some options are only “Good One Side” so if you install it “upside-down” the imperfections can damage the mattress. This is only an issue if you have a two-sided mattress that you flip each month.

Mattresses have been installed in RVs and travel trailers for decades. My father has a 1974 Airstream trailer with the original mattress that is installed on plywood. And it has been abused as a hunting camp for about 20 years and still has no mold issues.

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1 thought on “Add Plywood to Bed Frame: Detailed Guide”

  1. How can you cover a 60″x80″ queen platform bed with only 1 sheet of 4’x8′ Plywood. It seems that I need more than one sheet.
    I have a metal 60×80 bed frame which has a center rib both vertically and horizontally. It also has slats
    with 7″ spacing. The foam mattress seems okay w/o plywood but requires no more than 2′ spacing and suggests full coverage. I plan to put on 1/4″ sandply (Home Depot) plywood. I’m not sure how to section it. Please see attached drawing.
    Solution 1 supports the middle but is where sleeping will likely occur. Solution 2 puts the small section near the wall but joint rests on the struts. (maybe no big deal). Solution 3 the joint is supported but if measurement is off the joint could be unsupported for 30″ (unlikely ). I wish plywood came in larger sheets. Anyway, your input or suggestions would be greatly appreciated. I have a hunch It doesn’t matter which I use. I will email you a drawing. Thnks


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