The Challenge
Camera sensor sizes are specified in millimeters by manufacturers — a full-frame sensor is 36×24mm, APS-C is roughly 23.5×15.6mm — but lens coverage circles, older format names, and some US photography guides still reference inches. The '1-inch sensor' in premium compacts is not actually 25.4mm wide; it's a legacy tube-size designation making it 13.2×8.8mm. This naming convention causes real confusion when cross-referencing sensor coverage, lens compatibility, and depth-of-field calculators. For actual dimensional conversion, divide millimeters by 25.4 to get inches. A 36mm sensor width = 36 ÷ 25.4 = 1.417 inches. But sensor format names like '1-inch' or '2/3-inch' are historical labels — they do not match the physical diagonal in inches.
Camera Sensor Sizes: mm to Inches Conversion
| Format Name | Dimensions (mm) | Width (in) | Height (in) | Diagonal (mm) | Crop Factor |
|---|---|---|---|---|---|
| Medium Format (GFX) | 43.8 × 32.9 mm | 1.724 in | 1.295 in | 54.74 mm | 0.79× |
| Full Frame (35mm) | 36.0 × 24.0 mm | 1.417 in | 0.945 in | 43.27 mm | 1.0× |
| APS-H (Canon 1D legacy) | 27.9 × 18.6 mm | 1.098 in | 0.732 in | 33.53 mm | 1.29× |
| APS-C (Nikon/Sony/Fuji) | 23.5 × 15.6 mm | 0.925 in | 0.614 in | 28.21 mm | 1.5× |
| APS-C (Canon) | 22.3 × 14.9 mm | 0.878 in | 0.587 in | 26.82 mm | 1.6× |
| Micro Four Thirds | 17.3 × 13.0 mm | 0.681 in | 0.512 in | 21.64 mm | 2.0× |
| 1-inch (premium compact) | 13.2 × 8.8 mm | 0.520 in | 0.346 in | 15.86 mm | 2.7× |
| 1/1.28-inch (flagship phone) | 9.8 × 7.3 mm | 0.386 in | 0.287 in | 12.20 mm | 3.6× |
| 1/1.56-inch (phone) | 7.6 × 5.7 mm | 0.299 in | 0.224 in | 9.50 mm | 4.6× |
| 1/2.3-inch (action cam/budget) | 6.17 × 4.55 mm | 0.243 in | 0.179 in | 7.66 mm | 5.6× |
| 1/3.2-inch (phone telephoto) | 4.54 × 3.42 mm | 0.179 in | 0.135 in | 5.68 mm | 7.6× |
Sensor Area Comparison: How Much Larger is Full Frame?
| Format | Area (mm²) | Area (in²) | vs Full Frame |
|---|---|---|---|
| Medium Format (GFX) | 1441 mm² | 2.233 in² | 1.67× larger |
| Full Frame | 864 mm² | 1.339 in² | baseline |
| APS-C (Nikon/Sony) | 367 mm² | 0.568 in² | 2.36× smaller |
| APS-C (Canon) | 332 mm² | 0.515 in² | 2.60× smaller |
| Micro Four Thirds | 225 mm² | 0.349 in² | 3.84× smaller |
| 1-inch sensor | 116 mm² | 0.180 in² | 7.45× smaller |
| 1/1.28-inch phone | 71.5 mm² | 0.111 in² | 12.1× smaller |
| 1/2.3-inch | 28.1 mm² | 0.044 in² | 30.7× smaller |
Why Sensor Format Names Don't Match Their Inch Measurements
The '1-inch', '2/3-inch', and '1/2.3-inch' sensor naming convention dates to 1950s Vidicon and Plumbicon broadcast camera tubes. The tube diameter was the spec that mattered for housing design, and the usable image circle was roughly 2/3 of the tube diameter. When solid-state sensors replaced tubes in the 1980s, engineers kept the old tube-size labels to simplify lens compatibility documentation. A camera labeled as using a '2/3-inch sensor' would accept lenses designed for the old 2/3-inch tube camera. Today the names persist purely as shorthand — they carry no dimensional meaning in inches. When you need the real physical size, look up the manufacturer spec sheet for sensor width × height in millimeters.
How to Find Your Camera's Actual Sensor Size
- Look up your camera model's spec sheet — search '[model name] sensor size mm' or check the manufacturer's website
- Note the dimensions listed as W × H in mm — e.g. 35.9 × 23.9mm for Sony A7 series
- Divide each dimension by 25.4 for the inch equivalent — 35.9 ÷ 25.4 = 1.413 inches wide
- Calculate diagonal: √(W² + H²) then divide by 25.4 — confirms which format class your sensor belongs to
- Cross-reference crop factor: full frame diagonal (43.27mm) ÷ your diagonal = your crop factor
Sensor Size Trade-offs: What the mm Difference Actually Means
Sensor Size Facts to Check Before Buying a Camera
- Confirm actual mm dimensions in the spec sheet — format names like '1-inch' are not literal
- Calculate crop factor if you're moving from another system — it affects every lens you own
- Check pixel pitch (sensor area ÷ megapixel count) — larger pixels generally handle noise better than more, smaller pixels
- Verify lens mount compatibility — APS-C lenses on full frame bodies vignette heavily outside the APS-C image circle
- For video: check if the camera uses full sensor width or applies an additional crop in video mode
Step-by-Step Workflow
Enter sensor dimension in millimeters — width, height, or diagonal
Inch equivalent appears instantly
Cross-reference against the format chart below to identify your sensor class
Specifications
- Formula
- inches = mm ÷ 25.4
- Full frame (36×24mm)
- 1.417 × 0.945 inches
- APS-C Nikon/Sony (23.5×15.6mm)
- 0.925 × 0.614 inches
- APS-C Canon (22.3×14.9mm)
- 0.878 × 0.587 inches
- Micro Four Thirds (17.3×13mm)
- 0.681 × 0.512 inches
- 1-inch sensor (13.2×8.8mm)
- 0.520 × 0.346 inches
- Crop factor (APS-C vs FF)
- 1.5× (Nikon/Sony), 1.6× (Canon)
Best Practices
- Sensor format names (1-inch, 2/3-inch) are legacy video tube designations — they do not equal physical diagonal in inches
- Full frame diagonal: 43.3mm = 1.704 inches — the '35mm' format name refers to film strip width, not sensor size
- Crop factor = full frame diagonal ÷ sensor diagonal: APS-C 1.5×, MFT 2×, 1-inch 2.7×
- Medium format: Fujifilm GFX sensor is 43.8×32.9mm = 1.724 × 1.295 inches
- Phone sensors: main cameras range from 1/1.28-inch (9.6×7.2mm) to 1/1.56-inch (7.6×5.7mm)
Frequently Asked Questions
Why is a '1-inch sensor' not actually 1 inch wide?
The 1-inch label comes from 1950s vidicon vacuum tube technology, where a 1-inch tube produced a usable image area of about 16mm diagonal. When CCD sensors replaced tubes, manufacturers kept the legacy naming. A '1-inch sensor' has a 15.86mm diagonal (13.2×8.8mm) — not 25.4mm. The same applies to 1/1.7-inch, 2/3-inch, and other fractional format names.
What is the actual size of a full frame sensor in inches?
A full frame sensor is 36×24mm, which converts to 1.417×0.945 inches. The diagonal is 43.27mm = 1.703 inches. The '35mm' format name refers to the total width of 35mm film including sprocket holes — the actual image area on that film was 36×24mm, which modern full frame sensors replicate.
How do I convert sensor diagonal from mm to inches?
Divide by 25.4. Calculate diagonal using Pythagoras first if you only have width and height: diagonal = √(width² + height²). For APS-C (23.5×15.6mm): diagonal = √(552.25 + 243.36) = √795.61 = 28.21mm ÷ 25.4 = 1.110 inches. For full frame: √(1296 + 576) = √1872 = 43.27mm ÷ 25.4 = 1.703 inches.
What sensor size is best for low light photography?
Larger physical sensor area collects more light — full frame (36×24mm, 864mm²) captures roughly 2.4× more light than APS-C (23.5×15.6mm, 366mm²) at the same aperture and ISO. Medium format is larger still. That said, sensor technology matters: a modern APS-C BSI sensor can outperform an older full frame sensor in real-world low light.
How does sensor size affect lens focal length?
Crop factor multiplies the effective field of view. A 50mm lens on an APS-C (1.5× crop) produces the field of view of a 75mm lens on full frame. On Micro Four Thirds (2× crop), the same 50mm lens behaves like 100mm. The focal length itself does not change — only the angle of view relative to full frame equivalency.
What is a medium format sensor size in inches?
Fujifilm GFX and Hasselblad X-series sensors measure 43.8×32.9mm = 1.724×1.295 inches, with a diagonal of 54.7mm = 2.154 inches. Phase One IQ4 uses 53.4×40mm = 2.102×1.575 inches. True large format film starts at 4×5 inches (101.6×127mm), vastly larger than any current digital sensor.
How do smartphone sensor sizes compare in mm and inches?
Flagship phone main cameras use sensors labeled 1/1.28-inch to 1/1.56-inch. The 1/1.28-inch sensor (iPhone 15 Pro main) measures approximately 9.80×7.34mm. The 1/1.56-inch sensor measures 7.60×5.70mm. These format names follow the same legacy tube convention — the actual physical diagonal is far smaller than the label implies.