diff --git a/arrow/src/array/array_union.rs b/arrow/src/array/array_union.rs
index 09cc1ab59fe..58444b9a8fd 100644
--- a/arrow/src/array/array_union.rs
+++ b/arrow/src/array/array_union.rs
@@ -387,7 +387,7 @@ mod tests {
 
     #[test]
     fn test_dense_i32() {
-        let mut builder = UnionBuilder::new_dense(7);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -447,7 +447,7 @@ mod tests {
     #[test]
     #[cfg_attr(miri, ignore)]
     fn test_dense_i32_large() {
-        let mut builder = UnionBuilder::new_dense(1024);
+        let mut builder = UnionBuilder::new_dense();
 
         let expected_type_ids = vec![0_i8; 1024];
         let expected_value_offsets: Vec<_> = (0..1024).collect();
@@ -489,7 +489,7 @@ mod tests {
 
     #[test]
     fn test_dense_mixed() {
-        let mut builder = UnionBuilder::new_dense(7);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int64Type>("c", 3).unwrap();
         builder.append::<Int32Type>("a", 4).unwrap();
@@ -539,7 +539,7 @@ mod tests {
 
     #[test]
     fn test_dense_mixed_with_nulls() {
-        let mut builder = UnionBuilder::new_dense(7);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int64Type>("c", 3).unwrap();
         builder.append::<Int32Type>("a", 10).unwrap();
@@ -587,7 +587,7 @@ mod tests {
 
     #[test]
     fn test_dense_mixed_with_nulls_and_offset() {
-        let mut builder = UnionBuilder::new_dense(7);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int64Type>("c", 3).unwrap();
         builder.append::<Int32Type>("a", 10).unwrap();
@@ -714,7 +714,7 @@ mod tests {
 
     #[test]
     fn test_sparse_i32() {
-        let mut builder = UnionBuilder::new_sparse(7);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -766,7 +766,7 @@ mod tests {
 
     #[test]
     fn test_sparse_mixed() {
-        let mut builder = UnionBuilder::new_sparse(5);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Float64Type>("c", 3.0).unwrap();
         builder.append::<Int32Type>("a", 4).unwrap();
@@ -829,7 +829,7 @@ mod tests {
 
     #[test]
     fn test_sparse_mixed_with_nulls() {
-        let mut builder = UnionBuilder::new_sparse(5);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append_null::<Int32Type>("a").unwrap();
         builder.append::<Float64Type>("c", 3.0).unwrap();
@@ -882,7 +882,7 @@ mod tests {
 
     #[test]
     fn test_sparse_mixed_with_nulls_and_offset() {
-        let mut builder = UnionBuilder::new_sparse(5);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append_null::<Int32Type>("a").unwrap();
         builder.append::<Float64Type>("c", 3.0).unwrap();
@@ -929,7 +929,7 @@ mod tests {
 
     #[test]
     fn test_union_array_validaty() {
-        let mut builder = UnionBuilder::new_sparse(5);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append_null::<Int32Type>("a").unwrap();
         builder.append::<Float64Type>("c", 3.0).unwrap();
@@ -939,7 +939,7 @@ mod tests {
 
         test_union_validity(&union);
 
-        let mut builder = UnionBuilder::new_dense(5);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append_null::<Int32Type>("a").unwrap();
         builder.append::<Float64Type>("c", 3.0).unwrap();
@@ -952,7 +952,7 @@ mod tests {
 
     #[test]
     fn test_type_check() {
-        let mut builder = UnionBuilder::new_sparse(2);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Float32Type>("a", 1.0).unwrap();
         let err = builder.append::<Int32Type>("a", 1).unwrap_err().to_string();
         assert!(err.contains("Attempt to write col \"a\" with type Int32 doesn't match existing type Float32"), "{}", err);
@@ -1009,14 +1009,14 @@ mod tests {
         }
 
         // Sparse Union
-        let builder = UnionBuilder::new_sparse(5);
+        let builder = UnionBuilder::new_sparse();
         let record_batch = create_batch(create_union(builder));
         // [null, 3.0, null]
         let record_batch_slice = record_batch.slice(1, 3);
         test_slice_union(record_batch_slice);
 
         // Dense Union
-        let builder = UnionBuilder::new_dense(5);
+        let builder = UnionBuilder::new_dense();
         let record_batch = create_batch(create_union(builder));
         // [null, 3.0, null]
         let record_batch_slice = record_batch.slice(1, 3);
diff --git a/arrow/src/array/builder/union_builder.rs b/arrow/src/array/builder/union_builder.rs
index 8ef5028afc8..f263fecf6f2 100644
--- a/arrow/src/array/builder/union_builder.rs
+++ b/arrow/src/array/builder/union_builder.rs
@@ -111,7 +111,7 @@ impl FieldData {
 /// use arrow::array::UnionBuilder;
 /// use arrow::datatypes::{Float64Type, Int32Type};
 ///
-/// let mut builder = UnionBuilder::new_dense(3);
+/// let mut builder = UnionBuilder::new_dense();
 /// builder.append::<Int32Type>("a", 1).unwrap();
 /// builder.append::<Float64Type>("b", 3.0).unwrap();
 /// builder.append::<Int32Type>("a", 4).unwrap();
@@ -131,7 +131,7 @@ impl FieldData {
 /// use arrow::array::UnionBuilder;
 /// use arrow::datatypes::{Float64Type, Int32Type};
 ///
-/// let mut builder = UnionBuilder::new_sparse(3);
+/// let mut builder = UnionBuilder::new_sparse();
 /// builder.append::<Int32Type>("a", 1).unwrap();
 /// builder.append::<Float64Type>("b", 3.0).unwrap();
 /// builder.append::<Int32Type>("a", 4).unwrap();
@@ -159,7 +159,17 @@ pub struct UnionBuilder {
 
 impl UnionBuilder {
     /// Creates a new dense array builder.
-    pub fn new_dense(capacity: usize) -> Self {
+    pub fn new_dense() -> Self {
+        Self::with_capacity_dense(1024)
+    }
+
+    /// Creates a new sparse array builder.
+    pub fn new_sparse() -> Self {
+        Self::with_capacity_sparse(1024)
+    }
+
+    /// Creates a new dense array builder with capacity.
+    pub fn with_capacity_dense(capacity: usize) -> Self {
         Self {
             len: 0,
             fields: HashMap::default(),
@@ -168,8 +178,8 @@ impl UnionBuilder {
         }
     }
 
-    /// Creates a new sparse array builder.
-    pub fn new_sparse(capacity: usize) -> Self {
+    /// Creates a new sparse array builder  with capacity.
+    pub fn with_capacity_sparse(capacity: usize) -> Self {
         Self {
             len: 0,
             fields: HashMap::default(),
diff --git a/arrow/src/array/equal/mod.rs b/arrow/src/array/equal/mod.rs
index 975fbd2b360..debb8e7240c 100644
--- a/arrow/src/array/equal/mod.rs
+++ b/arrow/src/array/equal/mod.rs
@@ -1370,7 +1370,7 @@ mod tests {
 
     #[test]
     fn test_union_equal_dense() {
-        let mut builder = UnionBuilder::new_dense(7);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -1380,7 +1380,7 @@ mod tests {
         builder.append::<Int32Type>("b", 7).unwrap();
         let union1 = builder.build().unwrap();
 
-        builder = UnionBuilder::new_dense(7);
+        builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -1390,7 +1390,7 @@ mod tests {
         builder.append::<Int32Type>("b", 7).unwrap();
         let union2 = builder.build().unwrap();
 
-        builder = UnionBuilder::new_dense(7);
+        builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -1400,7 +1400,7 @@ mod tests {
         builder.append::<Int32Type>("b", 7).unwrap();
         let union3 = builder.build().unwrap();
 
-        builder = UnionBuilder::new_dense(7);
+        builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -1417,7 +1417,7 @@ mod tests {
 
     #[test]
     fn test_union_equal_sparse() {
-        let mut builder = UnionBuilder::new_sparse(7);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -1427,7 +1427,7 @@ mod tests {
         builder.append::<Int32Type>("b", 7).unwrap();
         let union1 = builder.build().unwrap();
 
-        builder = UnionBuilder::new_sparse(7);
+        builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -1437,7 +1437,7 @@ mod tests {
         builder.append::<Int32Type>("b", 7).unwrap();
         let union2 = builder.build().unwrap();
 
-        builder = UnionBuilder::new_sparse(7);
+        builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
@@ -1447,7 +1447,7 @@ mod tests {
         builder.append::<Int32Type>("b", 7).unwrap();
         let union3 = builder.build().unwrap();
 
-        builder = UnionBuilder::new_sparse(7);
+        builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int32Type>("b", 2).unwrap();
         builder.append::<Int32Type>("c", 3).unwrap();
diff --git a/arrow/src/compute/kernels/cast.rs b/arrow/src/compute/kernels/cast.rs
index 4f59c00fcb5..2d9e0b5ded7 100644
--- a/arrow/src/compute/kernels/cast.rs
+++ b/arrow/src/compute/kernels/cast.rs
@@ -5367,7 +5367,7 @@ mod tests {
     }
 
     fn make_union_array() -> UnionArray {
-        let mut builder = UnionBuilder::new_dense(7);
+        let mut builder = UnionBuilder::with_capacity_dense(7);
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Int64Type>("b", 2).unwrap();
         builder.build().unwrap()
diff --git a/arrow/src/compute/kernels/filter.rs b/arrow/src/compute/kernels/filter.rs
index 95a1bfa4da4..0bffee62cd9 100644
--- a/arrow/src/compute/kernels/filter.rs
+++ b/arrow/src/compute/kernels/filter.rs
@@ -1553,7 +1553,7 @@ mod tests {
         let c = filter(&array, &filter_array).unwrap();
         let filtered = c.as_any().downcast_ref::<UnionArray>().unwrap();
 
-        let mut builder = UnionBuilder::new_dense(1);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         let expected_array = builder.build().unwrap();
 
@@ -1563,7 +1563,7 @@ mod tests {
         let c = filter(&array, &filter_array).unwrap();
         let filtered = c.as_any().downcast_ref::<UnionArray>().unwrap();
 
-        let mut builder = UnionBuilder::new_dense(2);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Int32Type>("A", 34).unwrap();
         let expected_array = builder.build().unwrap();
@@ -1574,7 +1574,7 @@ mod tests {
         let c = filter(&array, &filter_array).unwrap();
         let filtered = c.as_any().downcast_ref::<UnionArray>().unwrap();
 
-        let mut builder = UnionBuilder::new_dense(2);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Float64Type>("B", 3.2).unwrap();
         let expected_array = builder.build().unwrap();
@@ -1584,7 +1584,7 @@ mod tests {
 
     #[test]
     fn test_filter_union_array_dense() {
-        let mut builder = UnionBuilder::new_dense(3);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Float64Type>("B", 3.2).unwrap();
         builder.append::<Int32Type>("A", 34).unwrap();
@@ -1595,7 +1595,7 @@ mod tests {
 
     #[test]
     fn test_filter_run_union_array_dense() {
-        let mut builder = UnionBuilder::new_dense(3);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Int32Type>("A", 3).unwrap();
         builder.append::<Int32Type>("A", 34).unwrap();
@@ -1605,7 +1605,7 @@ mod tests {
         let c = filter(&array, &filter_array).unwrap();
         let filtered = c.as_any().downcast_ref::<UnionArray>().unwrap();
 
-        let mut builder = UnionBuilder::new_dense(3);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Int32Type>("A", 3).unwrap();
         let expected = builder.build().unwrap();
@@ -1615,7 +1615,7 @@ mod tests {
 
     #[test]
     fn test_filter_union_array_dense_with_nulls() {
-        let mut builder = UnionBuilder::new_dense(4);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Float64Type>("B", 3.2).unwrap();
         builder.append_null::<Float64Type>("B").unwrap();
@@ -1626,7 +1626,7 @@ mod tests {
         let c = filter(&array, &filter_array).unwrap();
         let filtered = c.as_any().downcast_ref::<UnionArray>().unwrap();
 
-        let mut builder = UnionBuilder::new_dense(2);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Float64Type>("B", 3.2).unwrap();
         let expected_array = builder.build().unwrap();
@@ -1637,7 +1637,7 @@ mod tests {
         let c = filter(&array, &filter_array).unwrap();
         let filtered = c.as_any().downcast_ref::<UnionArray>().unwrap();
 
-        let mut builder = UnionBuilder::new_dense(2);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append_null::<Float64Type>("B").unwrap();
         let expected_array = builder.build().unwrap();
@@ -1647,7 +1647,7 @@ mod tests {
 
     #[test]
     fn test_filter_union_array_sparse() {
-        let mut builder = UnionBuilder::new_sparse(3);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Float64Type>("B", 3.2).unwrap();
         builder.append::<Int32Type>("A", 34).unwrap();
@@ -1658,7 +1658,7 @@ mod tests {
 
     #[test]
     fn test_filter_union_array_sparse_with_nulls() {
-        let mut builder = UnionBuilder::new_sparse(4);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append::<Float64Type>("B", 3.2).unwrap();
         builder.append_null::<Float64Type>("B").unwrap();
@@ -1669,7 +1669,7 @@ mod tests {
         let c = filter(&array, &filter_array).unwrap();
         let filtered = c.as_any().downcast_ref::<UnionArray>().unwrap();
 
-        let mut builder = UnionBuilder::new_sparse(2);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("A", 1).unwrap();
         builder.append_null::<Float64Type>("B").unwrap();
         let expected_array = builder.build().unwrap();
diff --git a/arrow/src/ipc/reader.rs b/arrow/src/ipc/reader.rs
index 8335fa4bc9e..086a5b15957 100644
--- a/arrow/src/ipc/reader.rs
+++ b/arrow/src/ipc/reader.rs
@@ -1627,7 +1627,7 @@ mod tests {
         let array1 = StringArray::from(vec!["foo", "bar", "baz"]);
         let array2 = BooleanArray::from(vec![true, false, true]);
 
-        let mut union_builder = UnionBuilder::new_dense(3);
+        let mut union_builder = UnionBuilder::new_dense();
         union_builder.append::<Int32Type>("a", 1).unwrap();
         union_builder.append::<Float64Type>("b", 10.1).unwrap();
         union_builder.append_null::<Float64Type>("b").unwrap();
@@ -1876,12 +1876,12 @@ mod tests {
 
     #[test]
     fn test_roundtrip_dense_union() {
-        check_union_with_builder(UnionBuilder::new_dense(6));
+        check_union_with_builder(UnionBuilder::new_dense());
     }
 
     #[test]
     fn test_roundtrip_sparse_union() {
-        check_union_with_builder(UnionBuilder::new_sparse(6));
+        check_union_with_builder(UnionBuilder::new_sparse());
     }
 
     /// Read gzipped JSON file
diff --git a/arrow/src/ipc/writer.rs b/arrow/src/ipc/writer.rs
index c817cb77c13..826e49ca87d 100644
--- a/arrow/src/ipc/writer.rs
+++ b/arrow/src/ipc/writer.rs
@@ -2040,7 +2040,7 @@ mod tests {
             ),
             true,
         )]);
-        let mut builder = UnionBuilder::new_sparse(5);
+        let mut builder = UnionBuilder::with_capacity_sparse(5);
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append_null::<Int32Type>("a").unwrap();
         builder.append::<Float64Type>("c", 3.0).unwrap();
diff --git a/arrow/src/util/pretty.rs b/arrow/src/util/pretty.rs
index 6f4d9e34a99..b92e658f1f2 100644
--- a/arrow/src/util/pretty.rs
+++ b/arrow/src/util/pretty.rs
@@ -649,7 +649,7 @@ mod tests {
 
     #[test]
     fn test_pretty_format_dense_union() -> Result<()> {
-        let mut builder = UnionBuilder::new_dense(4);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Float64Type>("b", 3.2234).unwrap();
         builder.append_null::<Float64Type>("b").unwrap();
@@ -690,7 +690,7 @@ mod tests {
 
     #[test]
     fn test_pretty_format_sparse_union() -> Result<()> {
-        let mut builder = UnionBuilder::new_sparse(4);
+        let mut builder = UnionBuilder::new_sparse();
         builder.append::<Int32Type>("a", 1).unwrap();
         builder.append::<Float64Type>("b", 3.2234).unwrap();
         builder.append_null::<Float64Type>("b").unwrap();
@@ -732,7 +732,7 @@ mod tests {
     #[test]
     fn test_pretty_format_nested_union() -> Result<()> {
         //Inner UnionArray
-        let mut builder = UnionBuilder::new_dense(5);
+        let mut builder = UnionBuilder::new_dense();
         builder.append::<Int32Type>("b", 1).unwrap();
         builder.append::<Float64Type>("c", 3.2234).unwrap();
         builder.append_null::<Float64Type>("c").unwrap();