BrainGain 40KG Octagon Adjustable Dumbbell review – Brute force

16 weights in one dumbbell, BrainGain's 40kg home weight lets you change from 2.5kg to 40kg with a twist of the handle

BrainGain 40KG Octagon Adjustable Dumbbell review
(Image credit: Matt Kollat/T3)
T3 Verdict

The BrainGain 40KG Octagon Adjustable Dumbbell is a versatile workout partner for strength workouts, thanks to its sturdy construction and extensive weight range. Better still, the evenly distributed increments allow you to progress more steadily than cheaper adjustable dumbbells. Highly recommended for beginner and intermediate lifters.

Reasons to buy
  • +

    Sturdy construction

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    Huge weights range lets you progress easily

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    Knurled handle

  • +

    Straightforward to use and easy to store

Reasons to avoid
  • -

    Twist mechanism could be smoother

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    Not available in the US/AU

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BrainGain advertises its 40KG Octagon Adjustable Dumbbell as "BY FAR the BEST adjustable dumbbell in the market", thanks to the build quality and design of these hefty home weights. And indeed, the dumbbell, featuring 8-sided weight plates, looks solid and offers an excellent weight range to help you progress in your workouts at home. It's a great addition to any home gym.

Is it the best adjustable dumbbell, though? The BrainGain 40KG Octagon Adjustable Dumbbell has its merits, but it's not without shortcomings, however small they might be (the shortcoming, not the merits). But even considering these niggles, I can't see a reason why anyone who needs space-saving home weights shouldn't consider BrainGain's top adjustable dumbbell. Should you get one? Read this BrainGain 40KG Octagon Adjustable Dumbbell to find out.

BrainGain 40KG Octagon Adjustable Dumbbell review: Price and availability

The BrainGain 40KG Octagon Adjustable Dumbbells are sold in pairs and are available to buy directly from BrainGain for a recommended retail price of £700 (approx. $864/AU$1,220). At the time of writing, the dumbbells were on offer and sold for only £590 (approx. $728/AU$1,027). BrainGain also sells an adjustable dumbbell rack compatible with BrainGain 40KG Octagon Adjustable Dumbbells for £110 (approx. $135/AU$191). The company has other adjustable weights (dumbbells and kettlebells) in its repertoire, with prices from £160 (approx. $197/AU$278) for a 12-kilo pair. Other miscellaneous equipment is also available on the website, including weight benches and Crossfit equipment (e.g. jump ropes).

BrainGain 40KG Octagon Adjustable Dumbbell review

(Image credit: Matt Kollat/T3)

BrainGain 40KG Octagon Adjustable Dumbbell review: Design

There are a few different approaches to adjustable dumbells, with BrainGain's home weight championing the 'twist handle' method, which is the most convenient way to change weights, at least right now. As the name suggests, you need to twist the handle of the dumbbells to pick up or lose weight plates from the plastic cradle the weights sit in when not in use.

The process is super simple, and the twisting mechanism works well. The BrainGain 40KG Octagon Adjustable Dumbbell's handle has a slight resistance, making it feel more sturdy, but it is also ever so slightly tricky to get the handle in the correct position. You see, when the twisting mechanism is more fluid, it's easy to tell when the grip clicks into place. Here, it's not impossible to over or under-twist the handle, which would result in the plates not unlocking and you not being able to lift the dumbbells from the cradle. It requires a bit more attention, that's all, and I'm sure once you get used to the dumbbells, the number of faulty twists will reduce significantly.

The BrainGain 40KG Octagon Adjustable Dumbbell can be adjusted between 2.5kg (5.5 lbs) and 40kg (88 lbs) in 2.5-kilo increments. This is a superb weight range, and considering the low minimum and the high max weight, the adjustable dumbbells allow for a lot of room for improvement, meaning that even beginners can use them for training and keep using them for years to come. 

The plates are the same size (ala BLK BOX Adjustable Dumbbell), with the weight setting displayed at the base of the plates (where they meet the handle). The build quality is excellent, and the plastic-covered plates feel rugged enough to withstand the friction of being picked up from the cradle repeatedly. The knurled metal handle is the icing on the cake – it really makes the BrainGain 40KG Octagon Adjustable Dumbbell feel premium and durable.

BrainGain 40KG Octagon Adjustable Dumbbell review

(Image credit: Matt Kollat/T3)

BrainGain 40KG Octagon Adjustable Dumbbell review: Workout performance

Adjustable dumbbells such as the BrainGain 40KG Octagon Adjustable Dumbbell are best suited for strength workouts; you know, bench press, overhead press etc. These exercises are meant to be performed in a slow and controlled fashion, unlike, let's say, a clean and jerk, where you move the weights quite quickly. Not to mention exercises like the renegade row, where you place your weight on the dumbbells.

And while BrainGain's home weight feels well-constructed enough, I still wouldn't do any of those exercises with it due to how the weight plates connect. Don't get me wrong; they aren't flimsy, but I feel the weight plates wouldn't like the friction generated by renegade rows. Plus, I don't think I would want to grate away the BrainGain 40KG Octagon Adjustable Dumbbell on my garage gym's floor, considering how much they cost.

For strength training, though, they work flawlessly, apart from the occasional twisting issues I mentioned above. The knurled handles are a joy to grip, and the weights feel balanced in hand. I thoroughly enjoyed that I could add tons of weight for bench presses, then instantly drop it for shoulder presses – supersets have never been easier! I liked the octagonal shape of the plates, not because of their functionality – adjustable weights rarely roll away when I pop them down on the floor – but because of their looks.

Speaking of changing weights: the best feature of the BrainGain 40KG Octagon Adjustable Dumbbells is that it allows for a granular change in weight. Some adjustable dumbbells will jump as much as 5 kilos (11 lbs) between different stops, but not this one. The different settings are 2.5kg, 5kg, 7.5kg, 10kg, 12.5kg, 15kg, 17.5kg, 20kg, 22.5kg, 25kg, 27.5kg, 30kg, 32.5kg, 35kg, 37.5kg, and 40kg; exactly 2.5 kg every time! Perfect.

BrainGain 40KG Octagon Adjustable Dumbbell review

(Image credit: Matt Kollat/T3)

BrainGain 40KG Octagon Adjustable Dumbbell review: Verdict

The BrainGain 40KG Octagon Adjustable Dumbbell is a versatile workout partner for strength workouts. It's a significant initial investment, but you have to remember that a pair of them replace 32 dumbbells, which would take up a lot more space and cost you a lot more money. Sure, Braingain's adjustable dumbbells are not quite as versatile as hex dumbbells, but no adjustable dumbbells are, so there is that.

The weights have a sturdy construction, and the weight range is out of this world. Better still, thanks to the evenly distributed increments, you won't have to worry about getting stuck in your progress because you can't build up the strength to jump to the next weight setting. The low minimum and high max weight settings will ensure both beginners and intermediate lifters can use the weights for their workouts.

Sadly, BrainGain currently don't ship their equipment to the US or Australia, only the UK and select European countries, which is a shame, but I appreciate that heavy home weights must be a real pain in the neck to ship overseas. If you happen to live in the UK, need a new pair of dumbbells for muscle building and have some money in your pocket, the BrainGain 40KG Octagon Adjustable Dumbbell is an excellent option.

BrainGain 40KG Octagon Adjustable Dumbbell review: Also consider

One of the closest competitors to the BrainGain adjustable dumbbells is the Core Fitness Adjustable Dumbbell. It's perfect for people who take muscle building at home seriously but can't afford a pair of Bowflex 552s. The Core Fitness unit feels more plasticky, but I still use them for home workouts years after I reviewed them, so they are durable enough for most workouts. Check out my Core Fitness Adjustable Dumbbell and Stand review.

The more digitally inclined of you should check out the JaxJox DumbbellConnect. This well-made and slick pair of smart dumbbells work effortlessly and boast a relatively decent weight range (8lbs-50Ibs/3.6kg-22.7kg). These digital home weights have their own companion app where you can keep track of your reps/sets and initiate workouts. Read Lee's full JaxJox DumbbellConnect review.

For functional workouts, I'd recommend the Boxbell 3-in-1 Adjustable Dumbbell. A pair of them replace 17 pieces of equipment, saving you a lot of space and money when building a compact home gym. It might not be as ergonomic as dedicated adjustable dumbbells and kettlebells, but considering how (comparatively) cheap and versatile it is, the Boxbell 3-in-1 is worth considering as a one-size-fits-all home weight. Read my full Boxbell 3-in-1 Adjustable Dumbbell review.

Matt Kollat
Section Editor | Active

Matt Kollat is a journalist and content creator who works for and its magazine counterpart as an Active Editor. His areas of expertise include wearables, drones, fitness equipment, nutrition and outdoor gear. He joined T3 in 2019. His byline appears in several publications, including Techradar and Fit&Well, and more. Matt also collaborated with other content creators (e.g. Garage Gym Reviews) and judged many awards, such as the European Specialist Sports Nutrition Alliance's ESSNawards. When he isn't working out, running or cycling, you'll find him roaming the countryside and trying out new podcasting and content creation equipment.