How to choose the best camera phone: sensor size vs megapixels

If you are looking for a new mobile phone it’s likely that a good camera will rank high on your list of must-have features. But how do you know if the camera on a phone is good or just ok? The way some phones and cameras are marketed, you’d think that the more megapixels they have the better the camera, but megapixels isn’t the best way to judge a smartphone camera. Megapixels can be a useful differentiator between different models, but there are other indicators of camera quality that you should keep in mind when choosing your next smartphone.

You might look at the range of smartphones on offer and wonder, ‘Is a 12-megapixel camera good enough? What’s the highest megapixel camera phone’ or you might be wondering ‘How many megapixels do I need for a good picture’. In this article we will try and answer those questions, as well as explain why it’s not how many megapixels that matters, but rather how big those pixels are.

What are megapixels?

A megapixel (MP) is equal to one million pixels (more or less, it’s actually 1,048,576 pixels).

The word pixel is made up of the words picture and element. Each pixel captures light and turns it into data. The data from the pixels is then combined to recreate the image.

You’d think that would mean the more pixels available, the more detailed the image, but not necessarily.

The data collected is made up of both good and bad information. The bad information is what we refer to as ‘noise’, that grainy, low colour, saturated appearance.

A 8 megapixel camera captures 8 million pixels, and a 12 megapixel camera will capture 12 million pixels.

Most phone cameras today offer 12MP. There are a few exceptions though, as we will discuss in our highest megapixel camera phone section below.

Is it better to have more megapixels?

Do more megapixels mean better photo quality? Not necessarily. If you are comparing an 8MP camera phone with a 12MP camera phone it may well be that the pictures you’d be able to take with the 12MP model would be better, but they could also be worse if the sensor is the same size. If both phones have an identically sized sensor then the pixels on the 12MP phone would need to be smaller in order to fit.

The problem here is that smaller pixels are more affected by noise. This is because while any size of pixel collects the same amount of noise, larger pixels also collect more of the other ‘good’ data needed to recreate the image.

One indication of how unnecessary it is to pile on the megapixels, Samsung’s Galaxy S5 and Galaxy S6 came with 16-megapixel sensors, while the S7, S8 and S9 models all offer 12MP. The key difference here was pixel size. Both phones had the same size sensor to pack all those pixels onto, so each pixel on the 16MP phone had to be smaller. The 16MP S6 had a 1.12µm pixel size compared to the 12MP S7 phone’s 1.4µm.

Picture shows: Galaxy S9

Another reason why you don’t necessarily want more megapixels is the file size. The more megapixels, the larger the file size and the more space the image will take on your phone. If your phone has a limited storage then a smaller file size will appeal. Large images will also take longer to upload.

This latter point may be less of an issue moving forward as there is a new image format being used that reduces file size. Apple has replaced the JPEG with the HEIF file format for photos and the HEVC (H.265) video format. These file types provide better, more efficient, compression. As a result, photos and videos take up less space.

Another reason why megapixels probably doesn’t matter is your plans for the photos you take. Will you be uploading them to Facebook or Twitter? Printing them out? Showing them off on your TV screen? Or plastering them on billboards around town? If you only intend to upload them to social networks, or share them via email or messages, then size really isn’t important (in fact it may be better if they are smaller as uploading them will take less time).

How big can you print?

While you might take photos and never look at them again, it’s likely you will be sharing them on social media, displaying them on your computer screen, or maybe even streaming them to your TV. You may also want to print them out. In that case a bit of maths will help you figure out just how big you will be able to print without ruining the quality of your image.

To take a couple of examples:

• A 12-megapixel image is 4000 pixels wide and 3000 pixels tall.
• An 8-megapixel image is 3456 pixels wide and 2304 pixels tall.

It’s the size of the pixels that is important here. You want those pixels to be printed as small as possible. Ideally you don’t want to be able to ‘see’ the pixels.

If you were to view the image on a screen, you would need to have around 144 pixels per inch (PPI) to get what Apple describes as ‘Retina’ quality. The idea of Apple’s Retina displays is that your eye isn’t able to distinguish the individual pixels.

So, if you wanted to view your image on a screen, at a ‘Retina’ resolution, your 8MP image couldn’t be shown larger than 24x16in, while a 12MP image would stretch to 27.8×20.85in. That might sound pretty big, but considering that 52in TVs are becoming more and more commonplace, it’s likely that you will want to view your image larger than the Retina resolution would allow.

Of course, when it comes to your TV screen you aren’t sitting right in front of it in quite the same way as you would with your laptop or iMac. So it’s likely that you could get away with a lower resolution unless you have amazing eyesight.

Wondering how many megapixels do you need for a good picture? It depends on the size of the photo.

When it comes to printing, the pixel density requirement tends to be much higher than that required for a screen, however, 150ppi would be the minimum for a photo print.

• At 150ppi, you could print an 8MP image at 23in x 15.4in
• At the same resolution, a 12MP image could be printed at 36.7in x 20in.

However, to get high-quality results, 300 pixels per inch would be the minimum.

• At 300dpi, your 8MP image could be printed at 11.5in x 7.7in.
• At 300dpi, the 12MP image could be printed at 13.3in x 10in.

Given that typical photo frames tend to be 8x6in or 10x8in, either of those photos would be big enough to fill that. But if you were hoping for something larger to hang over your fireplace, you may be out of luck.

If you have a different sized print in mind, this is how to work out how many pixels you will need:

How to work out how many pixels are needed for an 8 x 10in print:

1. Multiply the width and the height by 300 to get the size in pixels. So, an 8 x 10in print would be 2,400 x 3,000 pixels. 
2. Multiply the width pixels by the height pixels: 2,400 x 3,000 = 7,200,000 pixels.
3. Divide that result by 1 million to get the number of megapixels you need = 7.2mp.

How many megapixels needed to print an A3 poster:

• Using inches (because it’s easier), multiply the width and the height by 300: 11.7 x 16.5in is 3,510 x 4,950
• So that’s, 3,510 x 4,950 = 17,374,500.
• Or 17.4MP.

How many megapixels needed to print 16x20in print:

• 4,800 x 6,000 = 28,800,000
• 28.8MP.

If you don’t need to print images out bigger than 10x8in, and you won’t be viewing them on a big screen, then you probably don’t need more than 12mp.

How many megapixels do you need for… 4k, 8K, HD, 1080p?

When it comes to screens, here are some figures that might be of interest:

• Full HD resolution, aka 1080p measures 1,920×1,080 pixels. So that’s 1,920 x 1,080 = 2,073,600 pixels (or 2MP).
• 4K resolution is 3,840 × 2,160 = 8.294,400 (or 8.3MP).
• 8K resolution is 7,680 × 4,320 = 33.177,600 (33.2MP).

So, if you are thinking of getting an 8K TV any time soon, you might want to bear that in mind.

Not that your 12MP image will look terrible on an 8K TV set, it may have some loss in quality, but given that 150dpi is likely adequate resolution from a distance, it’s unlikely that it will look truly dreadful (unless you are a truly dreadful photographer).

Why you might want more megapixels

The only reason you might like a few more pixels is if you wanted to crop your shot. If you think this is a likely scenario, another thing to consider when looking for a camera phone is whether it has an optical zoom (as opposed, or in addition to a digital zoom), as this will enable you to frame the shot without cropping out pixels.

An optical zoom does not lose image quality because the same number of pixels are captured when the image is magnified. A digital zoom digitally magnifies the image. Rather than use the digital zoom you might as well use editing software to zoom in on the image afterwards, the results would probably be better.

Picture shows: Edit your photo after taking it

The highest megapixel camera phone

If despite what we have said above you are still looking for the maximum amount of megapixels, then you need to consider an SLR camera, rather than relying on a phone.

For the maximum amount of megapixels you’d be looking at the Canon EOS 5DS or 5DS R cameras that boast a jaw-dropping 50.6MP. Second to that is the Pentax 645Z with 51.4MP. Other top-of-the-range SLRs offer upwards of 36mp.

Canon has said it’s developing an SLR camera that can take 120MP shots. But it will be a while before that appears on the market. And when it does, you’d need a big memory card as RAW shots are a staggering 210MB each.

As for the most megapixels you can get on a smartphone:

• Nokia Lumia 1020 boasts 41MP (38MP).
• Moto Z Force offers 21MP.
• Asus ZenFone AR offers 23MP.
• OnePlus 5 offers a dual-camera set up with 16MP and 20MP sensors.
• Sony Xperia XZ Premium offers 19MP.
• Huawei P10 offers dual cameras with 12MP and 20MP (the latter is monochrome)
• iPhone X offers 12MP, as does the iPhone 8 and 8 Plus.

As we said above, 12MP is a pretty standard offering across the industry. This is probably because due to the size limit of a phone form-factor, sensors need to be tiny, and as a result packing on those millions of pixels means a smaller pixel size.

How to choose a good camera phone

If megapixels are just a myth, then what should you look for in a camera phone? Below we will look at some of the features we think are the most important.

Sensor size and pixel size

As we mentioned above, because phones are smaller than SLR cameras they can’t have large sensors, which means that pixels have to be small. The more pixels you squeeze onto a sensor, the smaller they need to be.

If you think of each pixel as a bucket, with the big buckets collecting more water. The water in this allegory is light (or photons). So bigger sensors are better because they allow for bigger pixels (although you could just have fewer pixels).

As Apple’s Phil Schiller said in the keynote announcing the iPhone 5S back in 2013: “Bigger pixels equal better picture”.

By increasing sensor size and pixel size manufacturers are able to make a big difference to low light sensitivity and noise. (Apple’s sensor in the iPhone 5s was 15% larger than that in the iPhone 5, hence making a big deal about this at the time of launch).

If you look at the world of SLR cameras, you may see sensors measured in width and height in millimetres, but in the world of contacts and smartphones, you will see sensors measured diagonally in fractions of an inch.

You’ll see measurements like this, from smallest to largest:

• 1/2.3in (6.3 x 4.7mm)
• 1/1.7in (7.6 x 5.7mm)
• 1in (13.2mm x 8.8mm)
• Micro Four Thirds or 4/3in (17.3 x 13mm)
• APS-C (23.5mm x 15.6mm)
• Full frame (36 x 24mm)

The sensors in the iPhone 8 and X are thought to measure 1/3in for the wide angle lens, and 1/3.6in for the telephoto lens in the Plus and X models. This is the same as the older 6s and 7 models. Apple hasn’t actually divulged this information, although it did say that the sensor was “bigger”.

Picture shows: iPhone X, iPhone 8 and iPhone 8 Plus

For comparative purposes:

• The sensor in Samsung Galaxy Note 8 and Samsung S9 sensors measure 1/3.6in
• LG’s V30 has a sensor measuring 1/3.1in
• Huawei’s P20 Pro uses a 1/1.7in sensor

But, it’s not just sensor size that matters, as we said above, the size of the pixel is crucial to how much good data can be collected by the camera.

As for pixel size, pixels are measured in micrometres or micron (written as μm).

As before, Apple hasn’t actually divulged the pixel size on its iPhone X or iPhone 8, but reports suggest that the wide-angle camera offers a 1.22µm pixel size (the same as the iPhone 6s), while the telephoto camera on the X and Plus models is 1.0µm. However, some other reports suggest that the iPhone X and 8 models have 1.4μm pixels.

For comparative purposes:

• Google’s Pixel 2 offers 1.4µm pixels.
• The Galaxy Note 8 and the Galaxy S9 both offer 1.4µm pixels on the wide angle camera, and 1.0µm on the telephoto camera.

Aperture

Another camera feature to look out for is the aperture. The aperture is the opening through which the camera lets in light. If you are attempting to take a photo in low-light you may benefit from an aperture that is able to let more light in, for example.

Aperture is represented by an f-number such as f/1.4, f/2, f/2.8, /f4, f/5.6, f/8, f/11, f/16, f/22, or f/32. The lower the f-number, the more light the lens lets in.

• The iPhone X has a ƒ/1.8 aperture on the wide-angle lens and ƒ/2.4 aperture on the telephoto.
• The iPhone 8 Plus has a ƒ/1.8 aperture on the wide-angle lens and ƒ/2.8 aperture on the telephoto.
• LG’s V30 has an f/1.6 rating.
• Samsung Galaxy S9 has a Dual Aperture that allows you to choose between f/2.4 and f/1.5.

Other features

There are many more features of a camera phone that can help it achieve a better photo, from the onboard editing software, to buzzwords such as True Tone Flash, Backside Illumination Sensor and Optical Image Stabilization. But the most important factor, when it comes to getting a good photo is, we think, the ability of the photographer. Read our tips on taking better photos here.