6 things you need to know about sensor size

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The size of the sensor in your camera is important, but bigger is not always better.

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Digital cameras are available in many formats, including the traditional “medium format” (the sort of camera that were frequently used by wedding photographers in the past). However, this is a consumer site, and as the average most consumer is not going to spend the sort of money needed to own such a camera (i.e. up to £30,000+ just for the camera body), we will limit this to camera sensors up to what is called “Full Frame”.

Full Frame?

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Lets start by stating what we mean by “Full Frame”. In the days of 35mm file cameras, a standard negative measured 36mm x 24mm. Digital camera sensors were (and still are) typically smaller that that – and often a lot smaller – because the larger the sensor the more expensive it is (duh) but there is more to it that that.

However, for clarity – “Full Frame” means the size of the camera sensor is basically the same size as a 35mm negative –  36mm x 24mm.

Other frame sizes?

I can bet that if I try to list every possible digital sensor size, I am bound to miss one. There are lots. So, given we are trying to debunk for the average consumer, I will endeavor to include the more popular sensor sizes. If there are any camera manufacturers reading this who want to include something, then let me know in the comments or ping me using the “contact us” page.

Note that the camera industry refers to “crop sizes” to more readily compare sensor sizes. Just like measuring TVs, the “crop size” is the comparison of the diagonal size of the thing. By convention a Full Frame has a crop size of ‘1’, and other sensors are measured as a proportion of that size. Remember, that a “crop” in photo terms means “make it smaller” by cropping the sizes so that convention is true here. Basically, the bigger the crop size number = the bigger the crop = and the smaller the sensor (upside-down  you might think – it’s the f-stop argument all over again for those who love that sort of thing).

For example: a full frame is 36mmx24mm = diagonal of (approx) 43mm. A “four thirds” sensor is (again approximately) 17mm x 13mm = diagonal of 21mm. Thus the “four thirds” sensor has a crop factor of 2. The diagonal is 1/2 that of full frame but importantly the surface area of the sensor is about 1/4 of that of the full frame sensor (which is good and bad at the same time).

Number madness?

The crop factor is important because it helps the consumer make an informed decision. Whether or not it’s the industry’s marketing departments trying to make things look better, but some of the sensor size numbers are not consumer-friendly.

A great example is with the smaller sensor sizes (in compact and super-zoom cameras). You will see sensor sizes like 1/3.2″, 1/2.5″ and 1/1.8″. What on earth? Once you work out what it means – it is (sort of) clearer.

  • 1/3.2 means the sensor (diagonal measurement) is 1″ (1 inch) divided by 3.2 – i.e about 8mm diagonal
  • 1/2.5″ means the sensor (diagonal measurement) is 1″ (1 inch) divided by 2.5 – i.e about 10mm diagonal
  • 1/1.8 means the sensor (diagonal measurement) is 1″ (1 inch) divided by 1.8 – i.e about 14mm diagonal

Marketing bunk strikes again – 1/3.2″ is SMALLER than 1/1.8″. What makes things even more confusing is that the resulting calculations (e.g. 8mm, 10mm, 14mm) are not always the actual size of the sensor. It would be easier (for those camera types) if the sensor size was quoted in straight mm (millimeters) to make life just that little bit easier for the consumer.

There is another factor at play – different manufacturers use the same terminology for different things. For example “APS-C” are different sizes depending upon the manufacturer. Although not widely different in this example (crop factors of 1.5 and 1.6 for APS-C), it does make a point that crop size is a key measure.

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Crop size round-up

This is a round-up of typical sizes. Note that different manufacturers may have slightly different specifications for their actual sensor size, so please check carefully what you might be buying. Remember to check the crop size of whatever you are buying!

Note that the “aspect ratio” (being the ratio of frame width the frame height) varies between the main sensor sizes (Full Frame and APS are usually 3:2, and other sizes are usually 4:3). This is not a major consideration factor but it’s worth knowing what you’re buying.

Sensor Diagonal
Crop Size Surface
Area (mm)
Area (factor)
Full Frame 43 1.0 864 1.00
APS-H 34 1.3 519 0.60
APS-C 28 1.5 368 0.43
27 1.6 329 0.38
1.5″ 23 1.9 262 0.30
Four Thirds 22 2.0 225 0.26
1″ 16 2.7 123 0.14
2/3″ 11 3.9 58 0.07
1/1.8″ 9 4.8 38 0.04
1/2.3″ 8 5.6 29 0.03
1/3.2″ 6 7.7 15 0.02

So, what’s the fuss?

Hopefully, we have debunked the terminology around sensor size. But in practice what does it mean? Well, the various “camps” will have their own views. And good for them. This is what we think in 6 areas:

1. Image quality

Each dot on the image is created by an individual dot (a “pixel”) on the sensor. Big pixels tend to be less ‘noisy’ which means they produce clearer images in low light or at very fast shooting settings (faster ISO speeds) and can produce a wider range of light to dark shades (the “dynamic range”). So, for any given number of pixels (the “megapixel” rating) the bigger sensor can have bigger pixels. If, for example, you photo a lot of dimly lit foxes at twilight, then a full frame will be better.

Bigger sensors = bigger pixels = lower noise, higher quality, more versatile, and better dynamic range.

On this quality point alone, I would choose a 12MP Full Frame over a 20MP compact every time. Excessive pixels (resulting in a higher resolution) are important when you have to heavily crop and edit images.

2. Focal length equivalents

When you buy a lens for a camera, quite often it will state the “35mm equivalent” (sometimes noted as “135 equivalent”). This is down to the crop size. For a bigger sensor, the angle of view has to be greater in order to project light across the span of the sensor. For a small sensor, the angle of view is therefore narrower. The human eye sees something like a 50mm lens would on a 35mm camera and that lens is often referred to as a ‘Standard Lens”.  With a smaller sensor, the same angle of view will require a wider lens.

The camera/lens makers state the 35mm equivalent to help in lens selection- which is really useful. I used a Four Thirds camera for a while (I know!….) and as a wildlife photographer was pleased with the 2X equivalent. The lenses were smaller and lighter for the same reach.

I have also used one of the super-zoom cameras which has a zoom up to 1480mm (equivalent to 830mm on a Full Frame). It was light to carry about, but the 1/2.3″ sensor was about 1/30th of the size of a full frame and quality suffered. However, it did enable me to zoom into things that would have cost me thousands on a Full Frame.

By the way – the focal length of the lens is exactly that. If you were to mount that lens on different cameras with different sensors, the focal length of that lens would not change. What is important is the angle of view.

Nonetheless, with different sensor sizes, the “equivalent” measure is useful when comparing systems. Yes, I know others will disagree totally with this point.

3. Flexibility

Apart from the obvious point that DSLRs have interchangeable lenses and are more of a “system” that fixed-lens/compact cameras, there are some other factors to consider:

  • The crop factor is a guide to the angle of view of the camera/sensor/lens. A Four Thirds sensor would – if other conditions are the same – capture only 1/2 the frame view of the Full Frame. The consideration is that to get the same angle of view, I would need a wider lens. Conversely to get close to a distant object is easier with a small sensor is it essentially is looking closer to start with.
  • A bigger sensor allows key items in the photo to be more easily isolated by blurring the other parts of the photo. Cameras with smaller sensors have a different dynamic needing a wider angle lens for the same framing of a larger sensor – and a wider angle means more depth of field and more difficult to isolate a item in the frame. A bigger sensor captures the same image with a longer focal length which has a narrower depth of field (making it easier to isolate a subject). The reverse is true, however, in that if you need a deeper depth of field then a bigger sensor is less capable with the same lens (although it could be a marginal difference).
  • A smaller sensor allows for a greater zoom range at a lower cost. The super-zoom/bridge cameras that offer a healthy zoom range must have a smaller sensor to work.

4. Weight and bulk

This touches on usability. Although a full frame camera may be the bees knees, try lumping it up a mountain with a couple of spare lenses. The above super-zoom bridge camera weighs in at 620gm all in. A full frame DSLR can outweigh that without a lens attached. The point is that you have to consider the purpose for the camera. If it’s to go mountaineering or long hikes, then maybe you might have to compromise – perhaps opt for an APS-C camera.

5. Intended use

This is really important. The focus is often on how many MP is available, but the sensor size is also important. Only you can decide on what to buy; but here are some questions you might like to pose when considering your purchase:

  • Will I have to carry the camera, lenses and its gubbins, and what camera will deliver the required quality for the lowest weight and bulk?
  • Will I be shooting sports? If so, check out the continuous shooting rates of the camera. A Full Frame camera has more (processing) work to do that an APS-C camera. That might impede the frame rate you can achieve.
  • What is the typical light situation? Low light, bright?
  • Am I mainly shooting portraits or landscapes?
  • What reach (angle of view) do I need. What lenses will I have to buy? You cannot take a detailed photo of a distant squirrel with a full frame sensor with a wide lens.
  • What range of lenses do you need? Do you need a big stack of lenses for a varied portfolio?
  • What will the images be used for? Web site or viewing on the home PC (where lower MP is fine) or printed magazine pages (which need high MP) ?
  • For the occasional image  – you could stick to using the mobile phone. I know someone who takes unbelievably good photos on his Google Pixel phone.

6. Cost

I have no idea actually how expensive it is to make a sensor. I have read they are very expensive to make, and also read that the sensor cost may be a ‘marketing factor’. Either way a big sensor is probably going to cost more than a small sensor.

However, a bigger sensor needs a bigger lens because, basically, there is more sensor-area to light up. So the bigger camera body, lenses, batteries etc etc are also going to add to the cost. Full Frame is going to be the most expensive camera system up to a crop size of 1. In fact they can be so expensive as to limit the Full Frame cameras to professionals, serious amateurs, and for that class of people of believe that they can big-it-up by parading expensive bits of kit to their friends – and probably have more money than sense.


OK, there is a lot to take in here. Buying any DSLR is a big purchase especially if upgrading to Full Frame which is a big, big, expensive step. So, take your time in balancing the various factors. I would love a Full Frame with a whole slew of lenses but it is, at least for me, not affordable.

For the pro portrait photographer then it’s an easy decision. For the enthusiastic out-and-abouter the APS-C format seem to strike a great balance between quality and cost; and for me (a photographer of over 40 years), I would not opt for anything smaller than an APS sized sensor.

One final thought – a great camera does not take great photos – a great photographer takes great photos.

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