diff --git a/docs/src/changelog.md b/docs/src/changelog.md
index c2bbf7a49..c14da9a0c 100644
--- a/docs/src/changelog.md
+++ b/docs/src/changelog.md
@@ -5,10 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
-## Unreleased
+## [unreleased]
 
 ### Fixed
-
+- Added missing BMI function `get_grid_size`, it is used for unstructured grids, for example
+  to get the length of arrays returned by BMI functions `get_grid_x` and `get_grid_y`.
+  
 ### Changed
 
 ### Added
diff --git a/src/bmi.jl b/src/bmi.jl
index 3f0c71979..0ef6e574a 100644
--- a/src/bmi.jl
+++ b/src/bmi.jl
@@ -338,6 +338,10 @@ function BMI.get_grid_node_count(model::Model, grid::Int)
     return length(active_indices(model.network, grids[grid]))
 end
 
+function BMI.get_grid_size(model::Model, grid::Int)
+    return length(active_indices(model.network, grids[grid]))
+end
+
 function BMI.get_grid_edge_count(model::Model, grid::Int)
     @unpack network = model
     if grid == 4
diff --git a/test/bmi.jl b/test/bmi.jl
index 979ff6284..36154e1b6 100644
--- a/test/bmi.jl
+++ b/test/bmi.jl
@@ -90,6 +90,10 @@ tomlpath = joinpath(@__DIR__, "sbm_config.toml")
             @test BMI.get_grid_node_count(model, 4) == 5809
             @test BMI.get_grid_node_count(model, 5) == 50063
             @test BMI.get_grid_node_count(model, 6) == 50063
+            @test BMI.get_grid_size(model, 1) == 2
+            @test BMI.get_grid_size(model, 4) == 5809
+            @test BMI.get_grid_size(model, 5) == 50063
+            @test BMI.get_grid_size(model, 6) == 50063
             @test minimum(BMI.get_grid_x(model, 5, zeros(Float, 50063))) ≈
                   5.426666666666667f0
             @test maximum(BMI.get_grid_x(model, 5, zeros(Float, 50063))) ≈