Camera listings love two numbers: sensor size and megapixels. “Full-frame”, “APS-C”, “Micro Four Thirds” and “1-inch” describe how big the light-capturing chip is, while megapixels describe how many pixels sit on it. The two are related but not the same, and mixing them up leads to poor buying decisions.
This explainer covers what each sensor format measures, what crop factor means, and how sensor size affects low light, background blur and file sizes, so you can compare a phone, a compact, a mirrorless camera or an action camera with clearer expectations.
Quick answer
- Full-frame is 36 x 24 mm, the reference size with a crop factor of 1.0.
- APS-C is about 23.6 x 15.6 mm (crop factor about 1.5), or 22.3 x 14.9 mm on Canon (1.6).
- Micro Four Thirds is 17.3 x 13 mm, with a crop factor of 2.0.
- 1-inch is about 13.2 x 8.8 mm, with a crop factor of about 2.7.
- A larger sensor collects more total light at the same settings, which usually means less noise.
- At the same framing and f-number, smaller sensors give deeper depth of field.
- More megapixels mean more detail and cropping room, but also larger files.
The main sensor sizes at a glance
The sizes below are typical imaging areas; exact dimensions vary slightly between models.
- Full-frame: 36 x 24 mm, about 864 sq mm, 3:2 shape. Named after 35 mm film.
- APS-C: about 23.6 x 15.6 mm (about 370 sq mm) on Nikon, Sony and Fujifilm; 22.3 x 14.9 mm (332 sq mm) on Canon. 3:2 shape.
- Four Thirds / Micro Four Thirds: 17.3 x 13 mm, 225 sq mm, 4:3 shape. Micro Four Thirds was launched by Olympus and Panasonic in 2008.
- 1-inch: about 13.2 x 8.8 mm, 116 sq mm, 3:2 shape. Used in premium compacts and some phones and pocket cameras.
- Smaller fractional sizes: phones and action cameras use sizes such as 1/1.3-inch or 1/2.3-inch. A 1/1.28-inch sensor, for example, is about 10.1 x 7.6 mm.
Area is what matters for light gathering. Using those figures, a full-frame sensor has roughly 2.3 times the area of a Nikon or Sony APS-C sensor, about 3.8 times that of Micro Four Thirds and about 7.4 times that of a 1-inch sensor.
Why a “1-inch” sensor is not one inch
Fractional-inch names come from old video camera tubes. The name described the outer diameter of the glass tube, not the light-sensitive area. A 1-inch sensor actually has a diagonal of about 16 mm, roughly two-thirds of an inch. The same naming logic applies to 1/1.3-inch and similar phone sizes, so do not read these numbers literally.
Crop factor explained
Crop factor is the ratio between the full-frame diagonal (about 43.3 mm) and a smaller sensor’s diagonal. It tells you how much narrower a lens’s view becomes on that sensor compared with full-frame.
Multiply focal length by crop factor to get the full-frame equivalent field of view. A 50 mm lens on a 1.5x APS-C camera frames like a 75 mm lens on full-frame. On Micro Four Thirds (2x), a 25 mm lens frames like 50 mm. This is why phone makers describe lenses as “24 mm equivalent”: the real focal length is much shorter, but the field of view matches a 24 mm lens on full-frame.
Crop factor does not change the lens, and it does not change exposure. An f/2.8 lens gives the same brightness at the same ISO and shutter speed on any sensor. The useful side effect is reach: a smaller sensor makes telephoto lenses frame tighter, which can help wildlife and sports shooters keep lenses smaller and lighter.
Low light and noise
At the same f-number, shutter speed and ISO, every sensor produces an equally bright image, but a larger sensor collects more total light to make it. DPReview’s equivalence explainer notes that full-frame gathers about four times the light of Four Thirds in that situation. More light relative to the random fluctuation in light (shot noise) generally means cleaner images, especially in dim interiors, evening events and weddings in poorly lit halls.
There are important caveats:
- Sensor generation, processing and noise reduction also affect results, so a newer small-sensor camera can beat an older large-sensor one.
- A faster lens can partly close the gap on a smaller sensor, though that also changes depth of field.
- In bright daylight, the difference between formats is often hard to see.
- Smartphones lean heavily on computational processing, which narrows the visible gap in many everyday scenes.
Depth of field and background blur
Depth of field (how much of the scene looks sharp) depends on the physical aperture size, focal length, distance and sensor size. To compare formats, you can multiply the f-number by the crop factor to get an “equivalent aperture” for depth of field. For example, a 50 mm f/2 lens on Micro Four Thirds frames and renders depth of field like a 100 mm f/4 lens on full-frame.
In practice, at the same framing and f-number, a larger sensor gives shallower depth of field and stronger background blur, which many portrait photographers like. A smaller sensor keeps more of the scene sharp, which can be an advantage for landscapes, group photos, close-ups and video where focus mistakes are less obvious. Neither is better in every case; it depends on what you shoot.
Remember that equivalent aperture is a comparison tool only. Use the real f-number for exposure.
Megapixels: what they do and do not do
Megapixels count the pixels in an image. A 24 MP photo is about 6,000 x 4,000 pixels, enough for a print of about 20 x 13 inches at 300 pixels per inch, which is plenty for most home prints and social media.
Higher megapixel counts help with large prints, heavy cropping and fine detail in landscapes or product photos. But they do not automatically mean better photos. Lens sharpness, focus accuracy, camera shake and lighting often limit detail first. On the same sensor size, more megapixels means smaller pixels, which are noisier individually, although at the same final print or screen size the overall difference is smaller than per-pixel views suggest.
Pixel binning on phones
Many phones advertise 48 MP, 50 MP or even 108 MP, but usually save smaller files by default. They combine groups of pixels into one larger virtual pixel, called pixel binning. Four-in-one binning turns a 48 MP sensor into 12 MP images; nine-in-one binning turns 108 MP into about 12 MP. Binned images are usually cleaner in low light, while full-resolution modes work best in bright light.
File sizes and storage
Megapixels drive file size, especially for RAW files. As one measured example, Photography Life reported that a RAW file from the 36.3 MP Nikon D810 was about 77 MB as 14-bit uncompressed, about 42 MB as 14-bit lossless compressed and about 33 MB as 12-bit lossless compressed. That is roughly 1 to 2 MB per megapixel, depending on settings. JPEG and HEIF files are much smaller, but sizes vary with scene detail and quality settings.
The practical effects: larger files fill memory cards faster, take longer to transfer and back up, and need a more capable computer for editing. If you shoot weddings or long trips in RAW, budget for extra cards and storage. Video file size, by contrast, depends mainly on resolution, frame rate and bitrate, not the photo megapixel figure.
How to choose: a practical checklist
- Shoot mostly in daylight and share online? A good phone or 1-inch compact may be enough.
- Want a light kit with long telephoto reach? Micro Four Thirds is worth a look.
- Want a balance of size, lens choice and image quality? APS-C suits many enthusiasts.
- Shoot events, low light or want maximum background blur? Full-frame has an edge, though bodies and lenses are generally larger and costlier.
- For megapixels, 20 to 30 MP suits most people; choose more only if you print large or crop heavily.
- Compare equivalent focal lengths and apertures when switching formats.
- Factor in storage and computer needs before choosing a very high-resolution camera.
Frequently asked questions
Is full-frame always better than APS-C?
Not always. Full-frame generally offers better low-light performance and shallower depth of field at the same framing. APS-C cameras and lenses are often smaller and lighter, and the crop factor helps telephoto reach.
Does a higher megapixel count mean better photos?
No. Megapixels add detail and cropping room, but lens quality, focus, light and technique usually matter more.
Does crop factor change the aperture or exposure?
No. An f/2.8 lens exposes the same on any sensor. Crop factor only changes field of view and, when you compare at the same framing, depth of field and total light.
What does “24 mm equivalent” on a phone mean?
It means the phone’s lens shows the same field of view as a 24 mm lens on a full-frame camera, even though its actual focal length is much shorter because the sensor is smaller.
