Pick the bunk and measure the ceiling. You get the headroom over the top bunk and who can sit up in it, the guardrail height the law asks for, the room on the bottom bunk, and the floor the bed takes.
Headroom over the top bunk
40″ over the top bunk: room to sit upeven for a tall adult · the guardrail's top at least 61″ from the floor · 31″ over the bottom bunk
Quick answer: a classic bunk bed is about 65″ tall and 81½″ long, 43″ wide for twin over twin and 57¾″ for twin over full (Max & Lily). Its top mattress sits about 51″ up, so an 8 ft ceiling leaves 40″ over a 5″ mattress: room for a tall adult to sit up. The law wants the guardrail 5″ above the mattress, and nobody under 6 on top.
How to use the bunk bed calculator
- Pick the bunk: twin over twin, twin over full or full over full.
- Measure the ceiling where the bed will stand.
- Enter the mattress you will use, and the top bunk’s slat height from your bed’s sheet if it is not 51″.
- Add the sleeper’s sitting height for a yes or no: sit them on the floor against a wall and measure to the top of the head.
The rules behind the numbers
The guardrail (the law)
16 CFR 1513, the US bunk bed rule: “The upper edge of the guardrails shall be no less than 5 inches (130 mm) above the top surface of the mattress when a mattress of the maximum thickness specified by the manufacturer’s instructions is on the bed.” The rule covers any bed whose foundation’s underside is “over 30 inches (760 mm) from the floor”, wants a guardrail on both sides of the top bunk, and tells parents: “Do not allow children under 6 years of age to use the upper bunk.”
The bed
Max & Lily’s classic bunks are 81.5″ long and 65″ tall; the twin over twin is 43″ wide, the twin over full and full over full 57.75″. Asked how high the top mattress sits, the maker answered: “The mattress sits about 51 inches off the floor.” It recommends 5″ mattresses and says: “We do not recommend exceeding a mattress thickness of 8 inches.”
Sitting up
ANSUR II, the US Army’s survey of 6,068 soldiers, measured sitting height from the seat to the top of the head: 95% of men sit under 38½″ (977 mm) and 95% of women under 35⅞″ (912 mm). A child sits shorter, so measure them.
How tall are bunk beds?
| Bed | Length × width | Height | Mattress |
|---|---|---|---|
| Max & Lily twin over twin | 81½″ × 43″ | 65″ | 5″, never over 8″ |
| Max & Lily twin over full | 81½″ × 57¾″ | 65″ | 5″, never over 8″ |
| Max & Lily full over full | 81½″ × 57¾″ | 65″ | 5″, never over 8″ |
| Max & Lily twin over twin low bunk | 81½″ × 54¼″ (with its ladder) | 50″ | 5″, never over 8″ |
| IKEA TUFFING twin | 77½″ × 40½″ | 51⅜″ | up to 5⅛″ |
| IKEA MYDAL twin | 77⅛″ × 41″ | 61¾″ | up to 8¼″ |
| IKEA VITVAL twin | 77½″ × 40½″ | 63¾″ | up to 5⅛″ |
From each maker’s product page, read 2026-09-29.
Headroom over the top bunk, by ceiling
| Ceiling | Over a 5″ mattress on 51″ slats | Who can sit up |
|---|---|---|
| 7 ft | 28″ | an adult cannot; measure a child |
| 7 ft 6 in | 34″ | about half of women; most men stoop |
| 8 ft | 40″ | even a tall adult |
| 9 ft | 52″ | even a tall adult |
Four worked examples
An 8 ft ceiling, a 5″ mattress. 40″ over the top bunk: room for a tall adult to sit up. The guardrail’s top must be at least 61″ from the floor.
The same bed with an 8″ mattress. 37″ of headroom, and the guardrail must reach 64″: 3″ higher.
A 7 ft basement ceiling. Only 28″ over the top bunk: an adult cannot sit up, and a child needs measuring first.
A child who sits 29″ tall, a 7′6″ ceiling. 34″ of headroom: they sit up with 5″ to spare.
Common bunk bed mistakes
- A thick mattress on top. Every inch comes off the guardrail’s 5″ and off the headroom.
- Measuring the bed’s height, not the mattress’s. The headroom starts on top of the mattress.
- A top bunk for a child under 6. The federal rule says no.
- The open guardrail against the wall. The continuous one goes on the wall side.
Next, the sheets and comforters that fit it: the free bedding size calculator. The free bedroom layout planner places the bunk in the room, and the 2D room planner draws the whole floor.
Its bedding sizesRead next
Bunk bed size and clearance questions
What are bunk bed dimensions?
Max & Lily’s classic bunks: 81½″ long and 65″ tall; 43″ wide for twin over twin and 57¾″ for twin over full or full over full. IKEA’s twin bunks are 77–78″ long, 40½–41″ wide and 51⅜–63¾″ tall.
How tall are bunk beds?
About 65″ for a classic bunk, 50″ for a low one (Max & Lily), and 51⅜ to 63¾″ for IKEA’s twin bunks. What matters for headroom is the top mattress’s height: about 51″ up on Max & Lily’s twin over full.
What is the bunk bed clearance to the ceiling?
The ceiling less the top of the top mattress. On 51″ slats with a 5″ mattress, an 8 ft ceiling leaves 40″, more than the 38½″ that 95% of men sit tall (ANSUR II); a 7 ft ceiling leaves 28″.
What ceiling height do you need for a bunk bed?
For anyone to sit up on a classic bunk: 8 ft, which leaves 40″ over a 5″ mattress. At 7 ft 6 in about half of women can and most men stoop; at 7 ft, only a child, so measure them sitting.
What are twin over full bunk bed dimensions?
Max & Lily’s: 81.5″ long, 57.75″ wide and 65″ tall, with the top mattress about 51″ off the floor and 36″ between the top and bottom bunk.
How high must a bunk bed guardrail be?
At least 5″ above the top of the thickest mattress the maker allows (16 CFR 1513.3). With a 5″ mattress on 51″ slats, that is 61″ from the floor.
How old should a child be for the top bunk?
6 or older: “Do not allow children under 6 years of age to use the upper bunk” (16 CFR 1513.6). Max & Lily asks the same for its top bunks and lofts.