diff --git a/conda/recipes/libcudf/meta.yaml b/conda/recipes/libcudf/meta.yaml
index 51b3e8afc05..c3e84447b3a 100644
--- a/conda/recipes/libcudf/meta.yaml
+++ b/conda/recipes/libcudf/meta.yaml
@@ -122,6 +122,7 @@ test:
     - test -f $PREFIX/include/cudf/join.hpp
     - test -f $PREFIX/include/cudf/lists/detail/concatenate.hpp
     - test -f $PREFIX/include/cudf/lists/detail/copying.hpp
+    - test -f $PREFIX/include/cudf/lists/count_elements.hpp
     - test -f $PREFIX/include/cudf/lists/extract.hpp
     - test -f $PREFIX/include/cudf/lists/gather.hpp
     - test -f $PREFIX/include/cudf/lists/lists_column_view.hpp
diff --git a/cpp/include/cudf/lists/count_elements.hpp b/cpp/include/cudf/lists/count_elements.hpp
new file mode 100644
index 00000000000..6b802d2ad5e
--- /dev/null
+++ b/cpp/include/cudf/lists/count_elements.hpp
@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2021, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <cudf/column/column.hpp>
+#include <cudf/lists/lists_column_view.hpp>
+
+namespace cudf {
+namespace lists {
+/**
+ * @addtogroup lists_elements
+ * @{
+ * @file
+ */
+
+/**
+ * @brief Returns a numeric column containing the number of rows in
+ * each list element in the given lists column.
+ *
+ * The output column will have the same number of rows as the
+ * input lists column. Each `output[i]` will be `input[i].size()`.
+ *
+ * @code{.pseudo}
+ * l = { {1, 2, 3}, {4}, {5, 6} }
+ * r = count_elements(l)
+ * r is now {3, 1, 2}
+ * @endcode
+ *
+ * Any null input element will result in a corresponding null entry
+ * in the output column.
+ *
+ * @param input Input lists column.
+ * @param mr Device memory resource used to allocate the returned column's device memory.
+ * @return New INT32 column with the number of elements for each row.
+ */
+std::unique_ptr<column> count_elements(
+  lists_column_view const& input,
+  rmm::mr::device_memory_resource* mr = rmm::mr::get_current_device_resource());
+
+/** @} */  // end of lists_elements group
+
+}  // namespace lists
+}  // namespace cudf
diff --git a/cpp/include/doxygen_groups.h b/cpp/include/doxygen_groups.h
index 03e00b881d8..1d796aca4b7 100644
--- a/cpp/include/doxygen_groups.h
+++ b/cpp/include/doxygen_groups.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, NVIDIA CORPORATION.
+ * Copyright (c) 2021, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -143,6 +143,7 @@
  * @defgroup lists_apis Lists
  * @{
  *   @defgroup lists_extract Extracting
+ *   @defgroup lists_elements Counting
  * @}
  * @defgroup nvtext_apis NVText
  * @{
diff --git a/cpp/src/lists/count_elements.cu b/cpp/src/lists/count_elements.cu
new file mode 100644
index 00000000000..78549152770
--- /dev/null
+++ b/cpp/src/lists/count_elements.cu
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2021, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <cudf/column/column.hpp>
+#include <cudf/column/column_device_view.cuh>
+#include <cudf/column/column_factories.hpp>
+#include <cudf/detail/null_mask.hpp>
+#include <cudf/detail/nvtx/ranges.hpp>
+#include <cudf/lists/count_elements.hpp>
+#include <cudf/lists/lists_column_view.hpp>
+#include <cudf/utilities/error.hpp>
+
+#include <rmm/cuda_stream_view.hpp>
+#include <rmm/device_vector.hpp>
+#include <rmm/exec_policy.hpp>
+
+#include <thrust/transform.h>
+#include <thrust/transform_scan.h>
+
+namespace cudf {
+namespace lists {
+namespace detail {
+/**
+ * @brief Returns a numeric column containing lengths of each element.
+ *
+ * @param input Input lists column.
+ * @param stream CUDA stream used for device memory operations and kernel launches.
+ * @param mr Device memory resource used to allocate the returned column's device memory
+ * @return New INT32 column with lengths.
+ */
+std::unique_ptr<column> count_elements(lists_column_view const& input,
+                                       rmm::cuda_stream_view stream,
+                                       rmm::mr::device_memory_resource* mr)
+{
+  auto device_column = cudf::column_device_view::create(input.parent(), stream);
+  auto d_column      = *device_column;
+  // create output column
+  auto output = make_fixed_width_column(data_type{type_to_id<size_type>()},
+                                        input.size(),
+                                        copy_bitmask(input.parent()),
+                                        input.null_count(),
+                                        stream,
+                                        mr);
+
+  // fill in the sizes
+  thrust::transform(rmm::exec_policy(stream),
+                    thrust::make_counting_iterator<cudf::size_type>(0),
+                    thrust::make_counting_iterator<cudf::size_type>(input.size()),
+                    output->mutable_view().begin<size_type>(),
+                    [d_column] __device__(size_type idx) {
+                      if (d_column.is_null(idx)) return size_type{0};
+                      auto d_offsets =
+                        d_column.child(lists_column_view::offsets_column_index).data<size_type>() +
+                        d_column.offset();
+                      return d_offsets[idx + 1] - d_offsets[idx];
+                    });
+
+  output->set_null_count(input.null_count());  // reset null count
+  return output;
+}
+
+}  // namespace detail
+
+// external APIS
+
+std::unique_ptr<column> count_elements(lists_column_view const& input,
+                                       rmm::mr::device_memory_resource* mr)
+{
+  CUDF_FUNC_RANGE();
+  return detail::count_elements(input, rmm::cuda_stream_default, mr);
+}
+
+}  // namespace lists
+}  // namespace cudf
diff --git a/cpp/tests/CMakeLists.txt b/cpp/tests/CMakeLists.txt
index 0d958f47b6b..106638a1a6f 100644
--- a/cpp/tests/CMakeLists.txt
+++ b/cpp/tests/CMakeLists.txt
@@ -653,6 +653,7 @@ ConfigureTest(AST_TEST "${AST_TEST_SRC}")
 # - lists tests ----------------------------------------------------------------------------------
 
 set(LISTS_TEST_SRC
+    "${CMAKE_CURRENT_SOURCE_DIR}/lists/count_elements_tests.cpp"
     "${CMAKE_CURRENT_SOURCE_DIR}/lists/extract_tests.cpp")
 
 ConfigureTest(LISTS_TEST "${LISTS_TEST_SRC}")
diff --git a/cpp/tests/lists/count_elements_tests.cpp b/cpp/tests/lists/count_elements_tests.cpp
new file mode 100644
index 00000000000..c5cb9d230c3
--- /dev/null
+++ b/cpp/tests/lists/count_elements_tests.cpp
@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2021, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <cudf/copying.hpp>
+#include <cudf/lists/count_elements.hpp>
+
+#include <cudf_test/base_fixture.hpp>
+#include <cudf_test/column_utilities.hpp>
+#include <cudf_test/column_wrapper.hpp>
+#include <cudf_test/type_lists.hpp>
+
+struct ListsElementsTest : public cudf::test::BaseFixture {
+};
+
+using NumericTypesNotBool =
+  cudf::test::Concat<cudf::test::IntegralTypesNotBool, cudf::test::FloatingPointTypes>;
+
+template <typename T>
+class ListsElementsNumericsTest : public ListsElementsTest {
+};
+
+TYPED_TEST_CASE(ListsElementsNumericsTest, NumericTypesNotBool);
+
+TYPED_TEST(ListsElementsNumericsTest, CountElements)
+{
+  auto validity = thrust::make_transform_iterator(
+    thrust::make_counting_iterator<cudf::size_type>(0), [](auto i) { return i != 1; });
+  using LCW = cudf::test::lists_column_wrapper<TypeParam>;
+  LCW input({LCW{3, 2, 1}, LCW{}, LCW{30, 20, 10, 50}, LCW{100, 120}, LCW{0}}, validity);
+
+  auto result = cudf::lists::count_elements(cudf::lists_column_view(input));
+  cudf::test::fixed_width_column_wrapper<int32_t> expected({3, 0, 4, 2, 1}, {1, 0, 1, 1, 1});
+  CUDF_TEST_EXPECT_COLUMNS_EQUAL(expected, *result);
+}
+
+TEST_F(ListsElementsTest, CountElementsStrings)
+{
+  auto validity = thrust::make_transform_iterator(
+    thrust::make_counting_iterator<cudf::size_type>(0), [](auto i) { return i != 1; });
+  using LCW = cudf::test::lists_column_wrapper<cudf::string_view>;
+  LCW input(
+    {LCW{"", "Héllo", "thesé"}, LCW{}, LCW{"are", "some", "", "z"}, LCW{"tést", "String"}, LCW{""}},
+    validity);
+
+  auto result = cudf::lists::count_elements(cudf::lists_column_view(input));
+  cudf::test::fixed_width_column_wrapper<int32_t> expected({3, 0, 4, 2, 1}, {1, 0, 1, 1, 1});
+  CUDF_TEST_EXPECT_COLUMNS_EQUAL(expected, *result);
+}
+
+TEST_F(ListsElementsTest, CountElementsSliced)
+{
+  auto validity = thrust::make_transform_iterator(
+    thrust::make_counting_iterator<cudf::size_type>(0), [](auto i) { return i != 1; });
+  using LCW = cudf::test::lists_column_wrapper<cudf::string_view>;
+  LCW input(
+    {LCW{"", "Héllo", "thesé"}, LCW{}, LCW{"are", "some", "", "z"}, LCW{"tést", "String"}, LCW{""}},
+    validity);
+
+  auto sliced = cudf::slice(input, {1, 4}).front();
+  auto result = cudf::lists::count_elements(cudf::lists_column_view(sliced));
+  cudf::test::fixed_width_column_wrapper<int32_t> expected({0, 4, 2}, {0, 1, 1});
+  CUDF_TEST_EXPECT_COLUMNS_EQUAL(expected, *result);
+}
+
+TYPED_TEST(ListsElementsNumericsTest, CountElementsNestedLists)
+{
+  std::vector<int32_t> validity{1, 0, 1, 1};
+  using LCW = cudf::test::lists_column_wrapper<TypeParam>;
+  LCW list({LCW{LCW{2, 3}, LCW{4, 5}},
+            LCW{LCW{}},
+            LCW{LCW{6, 7, 8}, LCW{9, 10, 11}, LCW({12, 13, 14}, validity.begin())},
+            LCW{LCW{15, 16}, LCW{17, 18}, LCW{19, 20}, LCW{21, 22}, LCW{23, 24}}},
+           validity.begin());
+
+  auto result = cudf::lists::count_elements(cudf::lists_column_view(list));
+  cudf::test::fixed_width_column_wrapper<int32_t> expected({2, 1, 3, 5}, {1, 0, 1, 1});
+  CUDF_TEST_EXPECT_COLUMNS_EQUAL(expected, *result);
+}
+
+TEST_F(ListsElementsTest, CountElementsEmpty)
+{
+  using LCW = cudf::test::lists_column_wrapper<cudf::string_view>;
+
+  LCW empty{};
+  auto result = cudf::lists::count_elements(cudf::lists_column_view(empty));
+  EXPECT_EQ(0, result->size());
+}