HTC has officially added the One A9 to its smartphone line up. The device offers a very premium looking build, which is similar to the iPhone 6 and iPhone 6S.

The One A9 isn't flagship in terms of specs but the design suggests otherwise. It's like the iPhone for Android, sort of.

We have crunched the numbers and compared the specs of the HTC One A9 and the Apple iPhone 6S to see what the differences are and how similar they really are when you take design away.

The HTC One A9 measures 145.8 x 70.8 x 7.3mm, which makes it slightly bigger and ever so slightly thicker than the Apple iPhone 6S that measures 138.3 x 67.1 x 7.1mm. They both have the same weight of 143g so nice and light.

Both these devices feature a metal body with a flat rear and rounded edges so in terms of actual design, they look pretty similar as we mentioned. They have plastic strips running across the top and bottom, but the HTC's rear camera is centralised while Apple's is to the left.

You'll find a fingerprint sensor on the front of both devices and they both come in four colours. The HTC One A9 comes in red, gold, grey and silver while the Apple iPhone 6S comes in rose gold, gold, silver and grey.

The HTC One A9 comes with a 5-inch display sporting a 1920 x 1080 resolution that delivers a pixel density of 440ppi. The Apple iPhone 6S on the other hand, comes with a slightly smaller 4.7-inch display but the resolution is also lower at 1334 x 750. This means a pixel density of 326ppi.

As the HTC One A9 has more pixels packed in per inch, it should mean slightly sharper and crisper images compared to the Apple iPhone 6S, although whether the human eye could notice it at this size is debatable.

We have had experience with both devices and they both perform well. Colours are brighter on the One A9 thanks to the AMOLED display but whites are whiter on the iPhone 6S, which overall offers a more natural display.

The HTC One A9 comes with a 13-megapixel rear camera that offers an aperture of F/2.0, built-in optical image stabilisation and a dual-tone flash. The front-facing camera is a 4-megapixel UltraPixel snapper.

The Apple iPhone 6S has a 12-megapixel rear camera with a smaller aperture of F/2.2 and what Apple calls a True Tone flash. There is no OIS built in for the iPhone 6S.

Smartphone camera performance isn't just about megapixels and features though. A lot comes down to the software and how the images are processed by the device after they have been shot.

The iPhone's cameras in the past have been highly acclaimed and the iPhone 6S is said to be the best yet. HTC has been criticised in the past for camera performance so it will be interesting to see how the One A9 does performs when we have completed our full review.

Hardware is difficult to compare as Apple doesn't release the same information as other manufacturers making spec-for-spec tricky. There is an octa-core Qualcomm Snapdragon 617 processor with 2GB or 3GB of RAM under the hood of the One A9.

The Apple iPhone 6S has the company's latest A9 processor with the M9 motion coprocessor but there are no official details on the RAM support. As the A9 processor is new and the SD617 is a mid-range chipset, it is likely that the iPhone will be more powerful than the One A9.

The HTC One A9 comes in 16GB and 32GB models, but it features microSD support for storage expansion up to 200GB. The Apple iPhone 6S doesn't offer microSD expansion, but internal storage options include 16GB, 64GB and 128GB. Future Android devices will see the microSD storage combined with the internal storage however, including the One A9, and therefore this means the HTC can offer more memory than the largest capacity iPhone 6S.

In terms of battery, the HTC One A9 comes with a 2150mAh capacity, which HTC claims will offer up to 16 hours of 3G talk time. Apple doesn't provide details on its capacities, but the iPhone 6S will apparently give you up to 14 hours of 3G talk time, which is a little less than the One A9.

The HTC One A9 comes with Android 6.0 Marshmallow with Sense 7 over the top. The HTC skin will offer a familiar experience for HTC users, but it has been refined slightly from previous versions with some of the bloatware removed. It means you get the latest Android experience but with a few extra additions rather than an overload.

The Apple iPhone 6S runs on iOS 9, which is an entirely different platform and to compare it to Android is like comparing chalk and cheese. Each of the two offer their own advantages so it's about what you prefer. There is more customisation within Android and a lot more devices to experience it on. You are restricted to iPhones if you want iOS but you'll get access to most new apps and services before Android users in many cases as everyone develops for iOS.

The HTC One A9 and the Apple iPhone 6S are very similar in terms of design, size and weight, but the iPhone 6S is a flagship device starting at £539 and the One A9 is aimed slightly lower, with a starting price of £429.

The One A9 has an extra megapixel on its rear camera, but this isn't to say it is a better camera. It does have a bigger and sharper display than the iPhone 6S however but as we mentioned, this also doesn't mean better.

The iPhone 6S has a smaller battery life, but a faster processor, while the One A9 has more storage and is a at least £90 cheaper. These two handsets are a prime example of how numbers aren't the only factor in which smartphone wins. Both devices look great so this is really about whether you want iOS or Android.