GSD Calculator
Ground Sample Distance (GSD) is the size of one pixel measured on the ground, the single most important accuracy metric in aerial imaging and drone mapping. Enter your camera sensor dimensions, focal length, image resolution and flight altitude, and this calculator returns GSD in cm/pixel, the on-ground image footprint, coverage area per frame, and the altitude needed to hit a target GSD. Choose a camera preset or enter custom sensor specs. Results update instantly as you type.
Formula
Worked example
A DJI Phantom 4 Pro (sensor 13.2 x 8.8 mm, focal length 8.8 mm, 5472 x 3648 px) flying at 80 m: GSD_w = (13.2 x 80 x 100) / (8.8 x 5472) = 2.19 cm/px. GSD_h = (8.8 x 80 x 100) / (8.8 x 3648) = 2.19 cm/px. Reported GSD = 2.19 cm/px (survey grade). Image footprint: 2.19 x 5472 / 100 = 119.8 m wide, 2.19 x 3648 / 100 = 79.9 m tall = 9,574 m2 per frame.
What is Ground Sample Distance?
Ground Sample Distance (GSD) is the distance on the ground represented by a single pixel in an aerial image. If your GSD is 3 cm/px, then adjacent pixels in the captured photo are 3 centimetres apart on the actual terrain below the drone. A smaller GSD means finer detail: a 1 cm/px image resolves features down to roughly 1 centimetre, while a 10 cm/px image can only distinguish objects about 10 centimetres apart. GSD is the primary metric for specifying, comparing and quality-checking aerial survey data, and it is reported in centimetres per pixel (cm/px) or millimetres per pixel in high-precision work.
How is GSD calculated?
The GSD formula links four camera parameters to flight altitude. For the horizontal axis: GSD_w = (sensor width in mm x altitude in m x 100) / (focal length in mm x image width in pixels). For the vertical axis: GSD_h = (sensor height in mm x altitude in m x 100) / (focal length in mm x image height in pixels). When the two axes give different results - which happens whenever the pixel pitch is not square or the sensor aspect ratio differs - the larger value is used as the reported GSD because it represents the coarser, less accurate dimension. Use the true focal length from your camera spec sheet, not the 35 mm equivalent, and use AGL (above-ground-level) altitude rather than ASL (above sea level).
Image footprint and coverage area
Once you know the GSD, the on-ground image footprint is straightforward: footprint width (m) = GSD (cm/px) x image width (px) / 100, and likewise for height. The product of footprint width and height gives the coverage area per frame. These numbers drive mission planning: if you know your target GSD and the area to survey, you can compute how many images are needed at a given overlap percentage. Typical survey flights use 75-80% forward overlap and 60-70% side overlap so that photogrammetry software has enough tie-points to build accurate mosaics and 3D models.
Reverse-solving: altitude for a target GSD
In practice, you often start from the required GSD and work backwards to find the flight altitude. Rearranging the width-axis formula gives: altitude (m) = (target GSD x focal length x image width) / (sensor width x 100). For example, a DJI Phantom 4 Pro with a target GSD of 1.5 cm/px requires: altitude = (1.5 x 8.8 x 5472) / (13.2 x 100) = 54.7 m AGL. This calculator does that reverse-solve automatically when you enter a target GSD in the input panel.
What affects GSD?
GSD improves (decreases) when you fly lower, use a longer focal length, increase megapixel count, or use a physically larger sensor. Flying at half the altitude halves the GSD, doubling detail. Doubling the focal length likewise halves the GSD, but narrows the field of view and so reduces coverage per image. Doubling the pixel count (doubling image resolution) also halves GSD. Choosing the right camera-altitude combination is a trade-off between resolution, coverage per pass and battery/time constraints. The interactive chart on this page shows how GSD changes across a range of altitudes for your current camera settings.
Typical GSD targets by application
| GSD range (cm/px) | Application | Example use case |
|---|---|---|
| < 1.5 | High precision | Engineering surveys, as-built documentation, crack detection |
| 1.5 - 3.0 | Survey grade | Topographic mapping, cadastral surveys, volume calculations |
| 3.0 - 5.0 | Mapping grade | Orthomosaic production, agriculture analytics, mine site mapping |
| 5.0 - 10.0 | Inspection grade | Corridor mapping, roof inspections, progress monitoring |
| > 10.0 | Reconnaissance | Large-area overview, preliminary site assessment |
Use these thresholds to choose the right flight altitude for your mission.
Frequently asked questions
What is a good GSD for drone mapping?
It depends on the application. High-precision engineering surveys typically target 1-2 cm/px. Topographic or cadastral surveys aim for 2-3 cm/px. General mapping and agriculture monitoring work well at 3-5 cm/px. Reconnaissance or corridor inspection can tolerate 5-10 cm/px. Anything above 10 cm/px is usually too coarse for anything other than a broad overview.
How does flight altitude affect GSD?
GSD is directly proportional to altitude. Doubling your altitude doubles your GSD (halves your resolution). Flying at 40 m instead of 80 m with the same camera gives half the GSD and four times the detail. The trade-off is that the image footprint shrinks proportionally, so you need more passes to cover the same area.
Should I use GSD width or GSD height?
When the two axes give different values, always report the larger one. It represents the coarser axis, so it is the conservative (worst-case) figure. Using the smaller value would overstate the resolution of the final image product.
What is the difference between GSD and resolution?
GSD is a measure of spatial resolution on the ground - how many centimetres one pixel represents. Image resolution (megapixels) describes how many pixels the sensor captures. A high-megapixel camera flown at very high altitude can still produce a large GSD (poor ground resolution). Both matter: high resolution shrinks GSD at a given altitude, but you still need to fly low enough to get the GSD your application requires.
Can I use GSD to work out how many images I need?
Yes. Once you know the image footprint (derived from GSD), divide the survey area by the footprint area, then multiply by the overlap factor. For 75% forward and 60% side overlap you need roughly 1 / (0.25 x 0.40) = 10 images per footprint area. Mission-planning apps like DJI Pilot, Pix4Dcapture, and DroneDeploy do this automatically, but understanding GSD lets you spot-check their estimates.
Does GSD apply to oblique or vertical images?
The standard GSD formula assumes nadir (straight-down) imaging where the camera is perpendicular to a flat ground plane. For oblique imagery, GSD varies across the frame: pixels near the horizon represent much more ground than pixels at the centre. For vertical structures such as building facades, the working distance is the horizontal range rather than the altitude. The formula still applies if you substitute horizontal range for altitude.