diff --git a/lib/microwaveprop/propagation/grid.ex b/lib/microwaveprop/propagation/grid.ex
new file mode 100644
index 00000000..724a198f
--- /dev/null
+++ b/lib/microwaveprop/propagation/grid.ex
@@ -0,0 +1,28 @@
+defmodule Microwaveprop.Propagation.Grid do
+  @moduledoc "CONUS grid definition for propagation scoring. 0.125 degree resolution (~14 km)."
+
+  @lat_min 25.0
+  @lat_max 50.0
+  @lon_min -125.0
+  @lon_max -66.0
+  @step 0.125
+
+  @doc "Returns all grid points as `{lat, lon}` tuples covering CONUS at 0.125 degree spacing."
+  def conus_points do
+    for lat <- float_range(@lat_min, @lat_max, @step),
+        lon <- float_range(@lon_min, @lon_max, @step) do
+      {Float.round(lat, 3), Float.round(lon, 3)}
+    end
+  end
+
+  @doc "Returns the grid step size in degrees."
+  def step, do: @step
+
+  @doc "Returns the CONUS bounding box as a map."
+  def bounds, do: %{lat_min: @lat_min, lat_max: @lat_max, lon_min: @lon_min, lon_max: @lon_max}
+
+  defp float_range(start, stop, step) do
+    count = round((stop - start) / step) + 1
+    Enum.map(0..(count - 1), fn i -> start + i * step end)
+  end
+end
diff --git a/lib/microwaveprop/propagation/grid_score.ex b/lib/microwaveprop/propagation/grid_score.ex
new file mode 100644
index 00000000..a5adc6b5
--- /dev/null
+++ b/lib/microwaveprop/propagation/grid_score.ex
@@ -0,0 +1,28 @@
+defmodule Microwaveprop.Propagation.GridScore do
+  @moduledoc false
+  use Ecto.Schema
+
+  import Ecto.Changeset
+
+  @primary_key {:id, :binary_id, autogenerate: true}
+
+  schema "propagation_scores" do
+    field :lat, :float
+    field :lon, :float
+    field :valid_time, :utc_datetime
+    field :band_mhz, :integer
+    field :score, :integer
+    field :factors, :map
+
+    timestamps(type: :utc_datetime)
+  end
+
+  @fields ~w(lat lon valid_time band_mhz score factors)a
+
+  def changeset(grid_score, attrs) do
+    grid_score
+    |> cast(attrs, @fields)
+    |> validate_required(@fields)
+    |> unique_constraint([:lat, :lon, :valid_time, :band_mhz])
+  end
+end
diff --git a/priv/repo/migrations/20260330214829_create_propagation_scores.exs b/priv/repo/migrations/20260330214829_create_propagation_scores.exs
new file mode 100644
index 00000000..6315c676
--- /dev/null
+++ b/priv/repo/migrations/20260330214829_create_propagation_scores.exs
@@ -0,0 +1,21 @@
+defmodule Microwaveprop.Repo.Migrations.CreatePropagationScores do
+  use Ecto.Migration
+
+  def change do
+    create table(:propagation_scores, primary_key: false) do
+      add :id, :binary_id, primary_key: true
+      add :lat, :float, null: false
+      add :lon, :float, null: false
+      add :valid_time, :utc_datetime, null: false
+      add :band_mhz, :integer, null: false
+      add :score, :integer, null: false
+      add :factors, :map, null: false
+
+      timestamps(type: :utc_datetime)
+    end
+
+    create unique_index(:propagation_scores, [:lat, :lon, :valid_time, :band_mhz])
+    create index(:propagation_scores, [:valid_time])
+    create index(:propagation_scores, [:band_mhz, :valid_time])
+  end
+end
diff --git a/test/microwaveprop/propagation/grid_score_test.exs b/test/microwaveprop/propagation/grid_score_test.exs
new file mode 100644
index 00000000..2945938c
--- /dev/null
+++ b/test/microwaveprop/propagation/grid_score_test.exs
@@ -0,0 +1,84 @@
+defmodule Microwaveprop.Propagation.GridScoreTest do
+  use Microwaveprop.DataCase, async: true
+
+  alias Microwaveprop.Propagation.GridScore
+
+  @valid_attrs %{
+    lat: 32.875,
+    lon: -97.0,
+    valid_time: ~U[2026-03-28 18:00:00Z],
+    band_mhz: 10_000,
+    score: 72,
+    factors: %{
+      "humidity" => 85,
+      "time_of_day" => 60,
+      "td_depression" => 70,
+      "refractivity" => 55,
+      "sky" => 80,
+      "season" => 65,
+      "wind" => 50,
+      "rain" => 90,
+      "pressure" => 45
+    }
+  }
+
+  describe "changeset/2" do
+    test "valid attributes" do
+      changeset = GridScore.changeset(%GridScore{}, @valid_attrs)
+      assert changeset.valid?
+    end
+
+    test "requires all fields" do
+      changeset = GridScore.changeset(%GridScore{}, %{})
+
+      assert %{
+               lat: ["can't be blank"],
+               lon: ["can't be blank"],
+               valid_time: ["can't be blank"],
+               band_mhz: ["can't be blank"],
+               score: ["can't be blank"],
+               factors: ["can't be blank"]
+             } = errors_on(changeset)
+    end
+
+    test "persists to database" do
+      changeset = GridScore.changeset(%GridScore{}, @valid_attrs)
+      assert {:ok, score} = Repo.insert(changeset)
+      assert score.lat == 32.875
+      assert score.lon == -97.0
+      assert score.band_mhz == 10_000
+      assert score.score == 72
+      assert score.factors["humidity"] == 85
+    end
+
+    test "enforces unique lat + lon + valid_time + band_mhz" do
+      assert {:ok, _} =
+               %GridScore{} |> GridScore.changeset(@valid_attrs) |> Repo.insert()
+
+      assert {:error, changeset} =
+               %GridScore{} |> GridScore.changeset(@valid_attrs) |> Repo.insert()
+
+      assert %{lat: ["has already been taken"]} = errors_on(changeset)
+    end
+
+    test "allows same location at different times" do
+      assert {:ok, _} =
+               %GridScore{} |> GridScore.changeset(@valid_attrs) |> Repo.insert()
+
+      later_attrs = Map.put(@valid_attrs, :valid_time, ~U[2026-03-28 19:00:00Z])
+
+      assert {:ok, _} =
+               %GridScore{} |> GridScore.changeset(later_attrs) |> Repo.insert()
+    end
+
+    test "allows same location and time for different bands" do
+      assert {:ok, _} =
+               %GridScore{} |> GridScore.changeset(@valid_attrs) |> Repo.insert()
+
+      other_band_attrs = Map.put(@valid_attrs, :band_mhz, 24_000)
+
+      assert {:ok, _} =
+               %GridScore{} |> GridScore.changeset(other_band_attrs) |> Repo.insert()
+    end
+  end
+end
diff --git a/test/microwaveprop/propagation/grid_test.exs b/test/microwaveprop/propagation/grid_test.exs
new file mode 100644
index 00000000..91e51190
--- /dev/null
+++ b/test/microwaveprop/propagation/grid_test.exs
@@ -0,0 +1,56 @@
+defmodule Microwaveprop.Propagation.GridTest do
+  use ExUnit.Case, async: true
+
+  alias Microwaveprop.Propagation.Grid
+
+  describe "conus_points/0" do
+    test "generates grid at 0.125 degree resolution" do
+      points = Grid.conus_points()
+      assert length(points) > 5000
+      assert length(points) < 100_000
+    end
+
+    test "all points within CONUS bounds" do
+      Enum.each(Grid.conus_points(), fn {lat, lon} ->
+        assert lat >= 25.0 and lat <= 50.0
+        assert lon >= -125.0 and lon <= -66.0
+      end)
+    end
+
+    test "points are on 0.125 degree grid" do
+      Enum.each(Grid.conus_points(), fn {lat, lon} ->
+        assert Float.round(lat * 8, 0) == lat * 8
+        assert Float.round(lon * 8, 0) == lon * 8
+      end)
+    end
+
+    test "first point is at SW corner" do
+      [{lat, lon} | _] = Grid.conus_points()
+      assert lat == 25.0
+      assert lon == -125.0
+    end
+
+    test "last point is at NE corner" do
+      points = Grid.conus_points()
+      {lat, lon} = List.last(points)
+      assert lat == 50.0
+      assert lon == -66.0
+    end
+  end
+
+  describe "step/0" do
+    test "returns 0.125" do
+      assert Grid.step() == 0.125
+    end
+  end
+
+  describe "bounds/0" do
+    test "returns CONUS bounding box" do
+      bounds = Grid.bounds()
+      assert bounds.lat_min == 25.0
+      assert bounds.lat_max == 50.0
+      assert bounds.lon_min == -125.0
+      assert bounds.lon_max == -66.0
+    end
+  end
+end