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Quick answer
A king mattress is 76 by 80 inches. A frame listed at 79.5 by 75.5 inches is a normal fit; the mattress sits about a quarter inch past each side. Check three things before you order: whether the frame needs a box spring on top (a tall platform frame does not), the total height with your mattress on it, and which weight rating the listing really commits to. If you want the lowest, simplest option, a metal frame that takes a box spring costs you the box spring. If you want a bed you can store things under, a tall platform frame is the one to read.
King mattress sizes and the number that matters
Amerisleep’s chart gives a king mattress as 76 by 80 inches, a surface area of 42.2 square feet, and says a king needs a room of about 12 by 12 feet. A California king is 72 by 84 inches, narrower and longer. Do not buy a king frame for a California king mattress or the reverse; see our California king bed frame guide for that size.
Worked example: floor area and sleeping height
Take the Amazon Basics metal frame, listed at 79.5 inches long and 75.5 inches wide. Its footprint is 79.5 times 75.5, which is 6,002.25 square inches, or 41.68 square feet when you divide by 144. The mattress itself is 76 by 80, which is 6,080 square inches or 42.22 square feet. So the frame is 0.54 square feet smaller than the mattress above it; the mattress overhangs by 0.25 inch on each side and by 0.25 inch at each end if you center it. That overhang is small, and the listing includes it in its own dimensions, so it is not a defect, but you cannot count on the frame sides to hold a king mattress in at the edges.
Now the sleeping height. The numbers below are our own arithmetic. We assume a 12 inch mattress and, for the box spring, 9 inches; those two assumptions are examples, not figures from any listing, so measure yours.
| Setup | Frame height | Box spring | Mattress | Top of mattress from floor |
|---|---|---|---|---|
| Amazon Basics metal frame | 7 in | 9 in (assumed) | 12 in (assumed) | 7 + 9 + 12 = 28 in |
| 20 inch platform frame | 20 in | none | 12 in (assumed) | 20 + 12 = 32 in |
| LIFEMENT wood platform | 12.1 in | none | 12 in (assumed) | 12.1 + 12 = 24.1 in |
If one sleeper has a knee or hip problem or the room has a low ceiling, those 8 inches between the lowest and highest setups matter more than the style.
What the three listings say
Amazon Basics Metal Bed Frame, 9-Leg Support Base, King, black (ASIN B07JZKSPY2). The table gives item dimensions of 79.5 by 75.5 by 7 inches, a weight of 17.95 pounds and metal material. The listing title says it is for box spring and mattress, so it needs a box spring on top; it does not say it supports a mattress alone. The bullets say it has 9 legs in 3 rows of 3 with a center bar, assembles without tools and “holds up to 700 lbs total (350 lbs per person max)”. The table says “Maximum Weight Recommendation 600 pounds”. Those two numbers disagree, so plan on 600 pounds. Best for: a low-cost frame when you already own a box spring. Watch out: it does not give you under-bed storage, only 7 inches in total.
20 Inch King Size Bed Frame, Double Layer Heavy Duty Metal Platform Tall (ASIN B0GJYN1PTS). The table gives 79.5 by 75.5 by 20 inches, a weight of 47.7 pounds and a rating of 4,000 pounds. The bullets give 16 inches of clearance under the frame, six mattress stoppers, rounded corners, three pre-drilled headboard holes in the rear legs and a no box spring design. Best for: someone who wants a tall bed with room underneath. Watch out: the listing’s table also shows 14, 16 and 18 inch versions with 10, 12 and 14 inches of clearance; be sure the 20 inch version is the one you add to the cart.
LIFEMENT King Bed Frame Classic Wood Platform, Espresso (ASIN B0H5G2CPKZ). The table gives 80 by 75.6 by 12.1 inches, a weight of 55.1 pounds, pine wood and a rating of 800 pounds. The bullets give 8.5 inches of under-bed clearance and a no box spring slat system compatible with memory foam, hybrid, latex and innerspring mattresses. Best for: a wood look at a lower height. Watch out: 8.5 inches of clearance fits a robot vacuum or flat bins, not a suitcase on its side.
How the three compare
| Listing | Needs box spring | Frame height | Under-bed clearance | Rating on the listing |
|---|---|---|---|---|
| Amazon Basics | Yes | 7 in | Not stated | 600 lb (table), 700 lb (bullets) |
| 20 inch platform | No | 20 in | 16 in | 4,000 lb |
| LIFEMENT wood | No | 12.1 in | 8.5 in | 800 lb |
The 4,000 pound rating is not comparable with the 600 pound rating as if the frame were seven times stronger; sellers measure and describe these ratings differently, and the listing does not explain how its number was reached. Use the rating only to make sure it exceeds the combined weight of the mattress and the sleepers.
How to pick, in order
1. Decide on a box spring first. If you already own a king box spring, the 7 inch metal frame uses it. If you do not, a platform frame saves the cost.
2. Write down the total height you want. Add frame height and mattress thickness, plus a box spring if you use one, as in the table above.
3. Check the width. Choose a frame listed at about 75.5 to 76 inches wide for a 76 inch mattress. If a listing gives a width well above that, find out whether it includes a headboard or side rails.
4. Check the storage claim. Only the under-bed clearance, not the frame height, tells you what fits underneath.
5. Check delivery. A king frame arrives in a heavy box. The three above weigh 17.95, 47.7 and 55.1 pounds.
Mistakes to avoid
Assuming a platform frame takes a box spring. A platform frame replaces it; adding one raises the bed by the box spring height and can leave you with a very high bed.
Trusting the headline weight rating. Read the table and the bullets; the Amazon Basics page shows two different numbers.
Buying by frame height. A 20 inch frame has 16 inches of clearance, so the frame itself takes up 4 inches.
Forgetting the headboard. The 20 inch frame has headboard holes but no headboard. See our headboards for queen beds and king size headboard guides for fitting one.
When a different frame is the better answer
If you want a frame that you can see from the front and that includes a headboard, read the platform bed frame guide and the solid wood bed frame guide. If you want a frame with drawers, see bed frame with storage. For a king bed that raises and lowers, the adjustable bed frame guide covers what a mattress needs. For the full list of king frames by style and room fit, see bedframe for king bed.
Frequently asked questions
What size frame fits a king mattress?
A king mattress is 76 by 80 inches per Amerisleep. The king frames above are listed at 75.5 to 76 inches wide and 79.5 to 80 inches long.
Do I need a box spring with a king frame?
Only if the frame says so. The Amazon Basics frame is made for a box spring and mattress; the two platform frames say no box spring is needed.
How high will my bed be?
Add the frame height and the mattress thickness, plus any box spring. With a 12 inch mattress the three setups above come to 28, 32 and 24.1 inches.
Is a 4,000 pound rating real?
The listing states it, but it does not say how it is measured. Treat it as a sign the seller used heavy steel, and check that the number is above the weight of the mattress and two sleepers.
Can I use a king mattress on a California king frame?
No. A king is 76 by 80 inches and a California king is 72 by 84 inches, so the king mattress would hang over the sides and fall short at the foot.
How much room does a king bed need?
Amerisleep recommends about 12 by 12 feet for a king.
Products (for Claude)
| ASIN | Name as on the listing | Two numbers from the listing | Listing URL |
|---|---|---|---|
| B07JZKSPY2 | Amazon Basics Metal Bed Frame, 9-Leg Support Base for Box Spring and Mattress, King-Size | 79.5 x 75.5 x 7 in; 17.95 lb | https://www.amazon.com/dp/B07JZKSPY2 |
| B0GJYN1PTS | 20 Inch King Size Bed Frame, Double Layer Heavy Duty Metal Platform Tall | 79.5 x 75.5 x 20 in; 47.7 lb | https://www.amazon.com/dp/B0GJYN1PTS |
| B0H5G2CPKZ | LIFEMENT King Bed Frame Classic Wood Platform, Espresso | 80 x 75.6 x 12.1 in; 55.1 lb | https://www.amazon.com/dp/B0H5G2CPKZ |
Products worth checking
We have not tested these products. Sizes and features come from the Amazon listings, checked on September 30, 2026; where a listing does not say, we say so.
Amazon Basics Metal Bed Frame, 9-Leg Support Base for Box Spring and Mattress, King-Size
The listing gives 79.5 x 75.5 x 7 in; 17.95 lb. We re-opened the page on September 30, 2026 and found these figures; other details are on the product page.
- Good for: comparing against the measurements in the guide above.
- Keep in mind: we have not tested it, and the listing may show more than one size or finish, so pick the variant that matches your numbers.
20 Inch King Size Bed Frame, Double Layer Heavy Duty Metal Platform Tall
The listing gives 79.5 x 75.5 x 20 in; 47.7 lb. We re-opened the page on September 30, 2026 and found these figures; other details are on the product page.
- Good for: comparing against the measurements in the guide above.
- Keep in mind: we have not tested it, and the listing may show more than one size or finish, so pick the variant that matches your numbers.
LIFEMENT King Bed Frame Classic Wood Platform, Espresso
The listing gives 80 x 75.6 x 12.1 in; 55.1 lb. We re-opened the page on September 30, 2026 and found these figures; other details are on the product page.
- Good for: comparing against the measurements in the guide above.
- Keep in mind: we have not tested it, and the listing may show more than one size or finish, so pick the variant that matches your numbers.
Sources checked
Specifications checked on September 30, 2026. Product details and availability can change, so confirm on the product page before you buy.
