King Single vs Double Bed: Size & Dimensions Guide (Australia)

In Australia, a king single mattress measures 107cm wide by 203cm long, and a double mattress measures 138cm wide by 188cm long. The double gives you 31cm more width, but the king single is 15cm longer. Which one suits you depends on who's sleeping in it, how much floor space the bedroom has, and whether length or width matters more for the sleeper. Below, we walk through the comparison and recommend which Koala mattress fits each sleeper type: teenagers, solo adults, couples on a budget, and guest-room setups.

Key Summary

• King single dimensions: 107cm wide by 203cm long. Best suited to teenagers, taller solo sleepers, and compact guest rooms.

• Double dimensions: 138cm wide by 188cm long. Best suited to couples on a budget, solo sleepers who want more width, and standard-sized guest rooms.

• The trade-off: the double is 31cm wider, the king single is 15cm longer. Prioritise width if two people are sharing; prioritise length if the sleeper is taller than about 180cm.

• Room size guidance: a king single fits comfortably in bedrooms as small as 2.5m by 3m. A double needs at least 3m by 3.5m for the same clearance around the bed.

• Bedding is different: king single and double sheets, quilts, and mattress protectors are not interchangeable. Factor bedding-cost differences into your decision.

King Single vs Double Comparison

Here's the side-by-side comparison, with dimensions, best-fit sleepers, and room-size guidance in one place.

The double has more total surface area (25,944 cm² compared to 21,721 cm² for the king single), but that extra area comes almost entirely from width. If length is what you need, the king single wins by 15cm.

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King Single vs Double Dimensions Breakdown

Both sizes follow Australian standard mattress dimensions, so the numbers are consistent across brands. Here's a closer look at each size, plus the practical difference in space a double gives you over a king single.

King Single Bed Dimensions (Length x Width in cm)

A king single mattress measures 107cm wide by 203cm long, or roughly 42 inches by 80 inches. It's noticeably wider than a standard single (which is 92cm wide) and the same length as a Queen or King. That extra length is the king single's defining feature: it fits sleepers up to around 195cm tall without their feet hanging off the end.

In our range, the Koala Mattress (Core) is the natural choice for growing kids and teens: its flippable design accommodates changing firmness preferences without replacing the mattress. 

For taller solo sleepers, the Koala Luxe adds 7 multi-layered support zones (per Luxe product page) at the same 107cm × 203cm king single size.

King single bed frames typically add another 10cm to 15cm to each dimension, so plan for a footprint of about 117cm x 213cm when you're working out room layout.

Double Bed Dimensions (Length x Width in cm)

A double mattress measures 138cm wide by 188cm long, or roughly 54 inches by 74 inches. It's 31cm wider than a king single but 15cm shorter. The shorter length matters: sleepers taller than about 180cm may find their feet close to or past the edge.

For couples choosing a double, the Koala Mattress (Core) is the natural fit: its flippable medium-firm / firm design lets each partner test both firmness levels within a single mattress. 

If body heat is an issue at night, the Koala Plus adds Cooling Gel Kloudcell® with CoolThread™ (13% cooler than leading online brands per Plus product page) at the same 138cm × 188cm double size.

Double bed frames typically add 10cm to 15cm on each side, so plan for a footprint of about 148cm x 198cm.

How Much Extra Space Does a Double Actually Give You?

The double gives you 31cm more width than a king single, but 15cm less length. That's a net gain of about 4,223 cm² of total surface area, which is roughly the size of a small pillow.

Practically, that extra width is meaningful if you sleep alone and prefer to spread out, or if you sometimes share the bed with a partner. But it's not enough to make a double bed comfortable for two adults on a permanent basis. Each sleeper gets 69cm of width on a double, which is narrower than a standard single bed. For two adults sharing every night, a queen (153cm wide, so 76cm each) is the more comfortable minimum.

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Who Is a King Single Bed For?

Teenagers and Growing Kids

A king single is the natural next step up from a standard single as a child grows. The extra 15cm of length matters: growth spurts push teens past the length of a standard single by about age 12 or 13. King single mattresses last through the teenage years without the sleeper's feet hanging off, and the compact width leaves floor space for a desk, wardrobe, and everything else a bedroom needs.

For growing children, a king single also holds resale or hand-down value: the length matches what a taller adult would want, so the mattress isn't outgrown as quickly.

Single Adults in Small Rooms or Studio Apartments

For solo sleepers in studio apartments, one-bedroom flats, or shared houses with compact bedrooms, a king single delivers a good balance: enough length for taller sleepers, without the floor-space cost of a double. Studio apartments especially benefit, because the extra width of a double can crowd out living-area furniture.

If you're between 180cm and 195cm tall and sleeping alone, a king single is usually more comfortable than a double, because length matters more than width when only one person is in the bed.

Guest Rooms and Multi-Purpose Spaces

Guest rooms that double as home offices, gyms, or hobby spaces benefit from king single beds. The compact width leaves the room usable for its second purpose during the week. Guests get a comfortable, standard-length sleep surface, and hosts don't lose the room to a bed that fills the floor.

A king single also fits under most standard bunk-bed frames, which makes it a strong choice for guest rooms that occasionally sleep two children or a parent-plus-child combination.

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Who Is a Double Bed For?

Couples on a Budget

For couples starting out (first apartment, uni share house, first home with a small bedroom), a double bed is often the smallest workable shared-bed size. It's tight for two adults, but it fits in bedrooms too small for a queen. Bedding is inexpensive and widely available. Bed frames are typically less costly than queen or king frames.

The trade-off is real: 69cm per person is narrower than each sleeper had on a single bed before they moved in together. Couples who value personal space at night usually upgrade to a queen within the first year or two.

Adults Who Want More Room to Move

Solo sleepers who move around a lot, sprawl across the bed, or share with a pet often prefer a double over a king single. The extra 31cm of width absorbs movement across the night: rolling from side to side, changing positions, or a cat claiming the corner all fit within a double's footprint.

For solo sleepers under about 175cm tall, a double is often more comfortable than a king single, because they don't need the extra length and they do value the width.

Guest Rooms Built for Two

Guest rooms designed to sleep couples (rather than solo guests) usually need at least a double bed. King single is too narrow for two adults; queen is more comfortable but takes more room. A double is the compromise: enough width for two guests for a few nights, without dominating the room.

If your guest room can accommodate a queen, that's the better long-term choice for couples. If the room can only fit a double, guests will still be comfortable for short stays.

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King Single vs Double: What's the Difference?

A king single measures 107cm wide by 203cm long. A double measures 138cm wide by 188cm long. The double is 31cm wider, but the king single is 15cm longer.

The width difference (31cm) matters for anyone who plans to share the bed or wants extra room to move at night. The length difference (15cm) is significant for anyone taller than about 180cm, and often the deciding factor for solo sleepers.

King singles suit growing kids, taller solo adults, and compact rooms. Doubles suit couples starting out, solo sleepers who spread out, and standard-sized guest rooms. Neither is universally better; the right choice depends on the sleeper, the room, and the intended use.

If you're comparing a king single to a standard single instead, see our Single bed base and mattress guide for that specific comparison.

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How to Choose Between a King Single and a Double

Room Size and Layout

Room size often makes the decision. A bedroom under 3m x 3m becomes cramped with a double bed: floor space for a wardrobe, drawers, or a study desk gets squeezed. A king single fits the same room with more clearance and room to move.

Larger bedrooms (3m x 3.5m or bigger) can accommodate either size. In that case, other factors take over.

Quick check: measure your bedroom, then use masking tape to mark out a rectangle of 148cm x 198cm (double footprint including frame) on the floor. If the tape rectangle leaves less than 60cm of clearance on the sides you need to access, the room is too small for a double.

Who's Sleeping In It, Now and In the Future

Match the bed to the sleeper you have now, plus the sleeper you'll likely have in five years.

• A child aged 5 to 10: king single is usually the right call. Long enough to last through the teenage years. Not so wide that it fills the room.

• A teenager or young adult: king single or double, depending on preference. A tall teen usually prefers the length of a king single. A teen who values space to spread out (or occasional overnight guests) may prefer a double.

• A solo adult: king single if you're tall or need the compact footprint. Double if you're average height and prefer more width.

• A couple planning to share: a double is the minimum, and a queen is the recommended long-term choice.

Budget and Bedding Costs

Purchase costs vary between mattress brands, but bedding costs are a real ongoing consideration.

• Sheet sets: widely available in both sizes. Doubles have a broader selection because they're a more common size across Australian households.

• Quilts and duvets: both sizes are widely stocked. Our duvet collection covers king single and double options.

• Mattress protectors: both sizes are standard, with no significant availability difference.

If bedding cost is a decision factor, doubles usually come out marginally cheaper per set because the size is more common. But the difference across a mattress lifespan (7 to 10 years) is typically less than a hundred dollars total, so it shouldn't be the primary decision driver.

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The Bottom Line: Which Should You Choose?

Choose a king single if:

• The sleeper is taller than about 180cm.

• The bedroom is compact (under 3m x 3m).

• The bed is for a growing child who's outgrowing a standard single.

• The room needs to work as a guest room plus a second function (office, gym, hobby space).

• You want a longer-lasting size that fits a taller adult later.

Choose a double if:

• The sleeper is under about 180cm and wants more width.

• The bed will occasionally sleep two people (couples on a budget, guest room for couples).

• The room can accommodate the wider footprint comfortably (at least 3m x 3.5m).

• The sleeper prefers to spread out or shares the bed with a pet.

If two adults will share the bed permanently, a queen is a stronger long-term choice than either a king single or a double. A double works for the first year or two of a shared bed, but many couples upgrade for the extra 15cm of width per person that a queen delivers.

Explore Koala's Bedroom Range

Whether you're setting up a first bedroom, upgrading a child's room, or refreshing a guest space, our bedroom range covers king single and double options across mattresses, bed bases, and coordinated bundles.

 Shop Koala Bedroom →

• Mattresses in king single and double sizes, all built on our all-foam Kloudcell® construction

• Bed bases designed to pair with our mattresses in both sizes

• Bedroom bundles that coordinate the mattress, bed base, and bedding in one package

• Duvets sized for king single, double, queen, and king beds

• Sofa beds for guest rooms that need to double as living spaces

Every Koala mattress includes a 120-night sleep trial and a 10-year warranty. Our Koala Mattress (Core) is ProductReview Mattress of the Year 2023, 2024, and 2025, a three-year streak, and our Koala SE is CHOICE®-Recommended.

Continue learning:

• Australian Bed Sizes Guide covering all six standard AU sizes

• Double Bed Base and Mattress for the double size deep-dive

• Best Mattress for Tall People if length is your key factor

• How to Choose a Mattress for the general buying framework