H3_EDGE_LENGTH

Return the average edge length of an H3 cell in meters for its resolution.

Category: h3Returns: DOUBLEDialect: Standard

Syntax

H3_EDGE_LENGTH(cell)

Description

## Overview Returns the average edge length of an H3 cell in meters at the cell's resolution. Because H3 cells are hexagons (plus twelve pentagons per resolution) tiling a sphere, the exact edge length varies slightly with location, but the variation is small at any given resolution. This function returns the published resolution-wide average, which is suitable for choosing a resolution by target scale, building rough distance estimates, and documenting cell sizes in metadata. Use it when you need a scale hint for a cell, for example to decide whether a resolution is fine enough to resolve an event or to estimate how many cells cover a corridor of a given width. ## Behavior - Returns a DOUBLE in meters. - Returns NULL if the input is NULL or not a valid H3 cell index. - The value depends only on the cell's resolution, not on its geographic location. - Pentagon cells have slightly shorter edges than surrounding hexagons at the same resolution; the returned average does not distinguish pentagons. - Deterministic: the same cell always returns the same edge length. - To get meters squared, use H3_CELL_AREA (edge length squared times approximately 2.598 for a hexagon). ## H3 resolution reference | Res | Average edge length | Average hex area | | --- | --- | --- | | 0 | 1,107,712 m (1,107 km) | 4.25 million km^2 | | 3 | 59,811 m (59.8 km) | 12,400 km^2 | | 5 | 8,544 m (8.54 km) | 253 km^2 | | 7 | 1,220 m (1.22 km) | 5.16 km^2 | | 9 | 174 m | 0.11 km^2 | | 10 | 65.9 m | 0.015 km^2 | | 12 | 9.4 m | 307 m^2 | | 15 | 0.5 m | 0.9 m^2 | ## Compatibility - Follows the standard H3 hierarchical hex grid specification for resolution-wise average edge lengths.

Parameters

Name	Type	Description
`cell`		Specifies the H3 cell index whose edge length to return. Must be a valid H3 cell.

Examples

-- Expect ~22,600 m at res 4, ~1,220 m at res 7, ~65.9 m at res 10.
SELECT
  H3_EDGE_LENGTH(H3_LATLNG_TO_CELL(52.5200, 13.4050, 4))  AS res4_m,
  H3_EDGE_LENGTH(H3_LATLNG_TO_CELL(52.5200, 13.4050, 7))  AS res7_m,
  H3_EDGE_LENGTH(H3_LATLNG_TO_CELL(52.5200, 13.4050, 10)) AS res10_m;

SELECT H3_EDGE_LENGTH(H3_LATLNG_TO_CELL(35.6762, 139.6503, 6)) / 1000.0 AS edge_km;

-- Pick the finest resolution whose edge is still larger than 500 m.
SELECT MAX(resolution) AS best_res
FROM (
  SELECT resolution,
         H3_EDGE_LENGTH(H3_LATLNG_TO_CELL(40.7128, -74.0060, resolution)) AS edge_m
  FROM (SELECT EXPLODE(SEQUENCE(0, 15)) AS resolution)
) t
WHERE edge_m >= 500;

-- A k-disk of radius k covers approximately k * edge_length meters.
SELECT h3_cell,
       3 * H3_EDGE_LENGTH(h3_cell) AS approx_k3_radius_m
FROM analytics.curated.h3_hourly_counts;

Pitfalls

The value is a resolution-wide average, not the exact edge length of the specific cell. Local variation is small (a few percent) but not zero.
Pentagon cells have shorter edges than hexagons at the same resolution, but this function returns the hexagon-average for both. If exact pentagon geometry matters, read H3_CELL_TO_BOUNDARY and compute edge lengths directly.
Edge length is not the same as cell radius. The distance from cell center to vertex equals edge length for a regular hexagon; the distance from center to edge midpoint is edge length times sqrt(3)/2.
The output is in meters. For kilometer-based reports divide by 1,000 explicitly at the call site to avoid unit mistakes.
NULL or invalid cells return NULL silently. Wrap with H3_IS_VALID_CELL when processing external input.