At some point, the transition out of a toddler bed becomes inevitable – and then comes the question of what to move into. A king single and a double bed might look similar at first glance, but they’re meaningfully different in size, and the right choice depends on your child’s age, how long you want the bed to last, and how much space you’re working with in the bedroom. Here’s how to think through the decision.

What Are the Actual Size Differences?

It helps to start with the numbers.

A king single bed measures approximately 107cm wide by 203cm long. It’s noticeably wider than a standard single (92cm), which makes it a comfortable step up for a growing child without taking up too much floor space.

A double bed measures approximately 138cm wide by 188cm long. It’s significantly wider than a king single – about 30cm more – but actually slightly shorter in length at 188cm compared to the king single’s 203cm.

That length difference is worth noting. Taller children or teenagers may find a double bed feels shorter than expected, while a king single gives more legroom despite being narrower.

What Age Is Each Size Best Suited To?

There’s no hard rule, but a few general guidelines apply.

King single beds tend to work well from around age 5 or 6 through to the early teenage years. They’re a natural next step after a standard single – big enough to feel grown-up, but compact enough to leave plenty of floor space for play in a child’s bedroom. For primary school-aged children, a king single is usually the most practical choice.

Double beds are better suited to older children and teenagers – typically from around 10 or 11 upwards, or whenever a child is starting to want a bedroom that feels less like a kid’s room and more like their own space. A double bed gives a teenager room to spread out, do homework in bed, or have a friend sleep over occasionally without the need for a separate mattress on the floor.

If your child is still in primary school, a double bed can feel oversized and may take up more room than is practical. If they’re heading into high school, a double starts to make more sense as a longer-term investment.

How Much Room Do You Have?

Room size often makes the decision for you.

As a guide, a bedroom should have at least 90cm of clearance on the sides of the bed you need to access, and enough space to open drawers or wardrobe doors without obstruction. For a king single, you need a minimum room size of roughly 2.5m x 3m to make this work comfortably. For a double, allow for at least 3m x 3.5m.

If the bedroom is on the smaller side, a king single is almost always the better choice. A double bed in a compact room can leave so little floor space that the room feels more like a corridor than a bedroom – and children need floor space to play, especially when they’re younger.

Measure the room before you decide, and use masking tape on the floor to mark out the bed footprint. It’s a simple step that removes a lot of guesswork.

Browse our king single bed frames and double bed frames to compare dimensions and styles side by side.

Will They Grow Into It?

It’s tempting to buy ahead and get a double bed for a seven-year-old on the basis that they’ll grow into it. In practice, this often means several years of a bed that’s too big for the room, too wide for the child, and takes up space that could be better used for play.

A more practical approach is to match the bed to where your child is now and plan to upgrade when they’re ready – typically around the start of high school. By that point, a double bed makes much more sense for their lifestyle, and you’ll get better use out of both purchases.

That said, if you’re buying for a child who is already 9 or 10 and you’re looking for something that will last through the teenage years without needing to replace it, a double is a reasonable investment. The key is being realistic about room size – a double only makes sense if the room can actually accommodate it comfortably.

Bunk Beds – A Third Option Worth Considering

If you have two children sharing a room, or if your child frequently has friends to stay, bunk beds are worth considering as an alternative to either a king single or a double.

A standard bunk bed fits two single or king single mattresses in roughly the same floor space as one – which makes them an exceptionally space-efficient solution for shared bedrooms. They also tend to be genuinely popular with children, who often see them as more fun than a standard bed.

The main consideration with bunks is ceiling height – you need enough clearance above the top bunk for a child to sit up comfortably without hitting the ceiling. Around 90-100cm above the top mattress is the minimum to aim for.

Take a look at our bunk beds if a shared room or sleepover-friendly setup is on your radar.

Final Thoughts

For most primary school-aged children, a king single is the right call – it’s a comfortable size upgrade from a standard single without overwhelming the room. For older children heading into their teenage years, a double starts to make more sense, provided the room can accommodate it. Measure your space first, think about how long you need the bed to last, and don’t be tempted to size up just for the sake of it. The right bed for your child is the one that fits the room, suits their age, and leaves enough space for them to actually live in.

For more help navigating bed sizes, our Australian bed size guide covers all standard mattress dimensions in detail.