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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchNASA measures a lunar crater’s diameter by defining which edge counts, measuring that boundary in calibrated imagery or topographic data, and converting the result to a ground distance. The choice of edge matters: the rim crest, inner rim, and outer wall can produce different diameters. For large-crater catalogs and shape studies, NASA also uses elevation measurements from the Lunar Orbiter Laser Altimeter (LOLA), not just photographs.
How an image measurement becomes a crater diameter
A measurement on a screen or printed image is not yet a real-world crater size. Scientists first need the image scale: the ground distance represented by a pixel or by a unit of printed length. They then measure across the chosen crater boundary and multiply that image distance by the scale.
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- Establish the scale. Use the image’s stated resolution or derive a scale from a known ground width and the image’s measured width.
- Define the boundary. Decide whether the measurement follows the rim crest, inner rim, outer wall edge, or another mapped feature.
- Measure across the crater. Record the image distance across the declared boundary.
- Convert to ground distance. Multiply the image distance by the scale and report the result in meters or kilometers, along with the boundary definition.
NASA’s Lunar Math, Version 3 gives an example: an image representing 16.6 kilometers across measures 134 millimeters on the page. Dividing the ground width by the printed width gives approximately 124 meters per millimeter. That scale can then be applied to features measured on the same image.
Why the selected edge changes the answer
A crater does not always have one crisp outline. Its raised rim, inner slope, and outer wall may each suggest a plausible edge, and erosion or lighting can make those boundaries harder to distinguish. A reported diameter is therefore more useful when it states what was measured.
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NASA’s Lunar Math answer key illustrates the difference with Alphonsus. In that classroom exercise, one edge choice gives an estimate of about 102 kilometers; measuring to the outermost crater-wall edge gives about 132 kilometers. These are estimates from that exercise’s image, not authoritative catalog values for the crater. The difference shows why two size figures should not be compared without checking their boundary definitions.
What image width and resolution tell you
Image scale provides context for how precisely a boundary can be located. NASA’s LROC examples span different fields of view: the Narrow Angle Camera frame of Concentric Crater is identified as 510 meters wide, while the Wide Angle Camera mosaic of Mendeleev Crater is reported at 100 meters per pixel and shows a crater 313 kilometers across.
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- Concentric Crater: a 510-meter-wide LROC Narrow Angle Camera frame.
- Mendeleev Crater: an LROC Wide Angle Camera mosaic at 100 meters per pixel, with the crater reported as 313 kilometers across.
These examples are not interchangeable measurement recipes. A frame’s width or pixel scale tells you the image’s ground coverage and resolution; the chosen crater boundary and the clarity of the feature still affect the result.
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How LOLA elevation data add a third dimension
Images show surface appearance, while LOLA—the Lunar Orbiter Laser Altimeter—provides elevation measurements. NASA uses LOLA data to support a catalog of large lunar craters and to study crater shape and depth-to-diameter relationships. Its “Counting Craters on the Moon” visualization depicts craters larger than 20 kilometers in diameter using LOLA data.
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Topographic measurements can help characterize a crater’s shape and depth, but depth-to-diameter relationships vary with crater type and planetary-body properties. NASA’s Drygalski Crater page describes using high-resolution LOLA topography to refine those relationships and constrain crater shape. A single universal depth ratio should not be assumed for every lunar crater.
Diameter and depth are different measurements
Diameter describes a horizontal distance across the surface; depth describes vertical relief. They may be derived from different evidence, so a width measurement does not by itself establish a crater’s depth.
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In its August 18, 2026 report on the Falcon 9 upper-stage impact, NASA said scientists measured the crater as 60 feet wide where the rim stood out in images. They estimated its depth at less than 10 feet using shadow length. That is an example tied to a specific impact and imagery, not a universal NASA depth-measurement protocol. The report explains how image lighting can make a rim or slope visible and how shadows can provide clues to relief.
How to read a reported crater size
When comparing two measurements, check whether they refer to the same dimension and the same mapped edge. A single image measurement, a classroom estimate, and a catalog entry based on topography may answer different questions even when each is described as a crater’s size.
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- Method: Was the figure measured from calibrated imagery or derived using elevation data?
- Boundary: Does it follow the rim crest, inner rim, outer wall, or another stated edge?
- Image context: What are the frame width and ground resolution?
- Dimension: Is the number a surface diameter or width, or a depth estimate?
- Scope: Is it a measurement of one visible crater, an educational exercise, or part of a larger-crater catalog?
Those details explain why NASA does not rely on one universal instrument or one boundary rule for every lunar-crater measurement. The method depends on the question being asked and the available imagery or topography.
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