diff --git a/compiler/gen_wasm/src/low_level.rs b/compiler/gen_wasm/src/low_level.rs
index cc5cff66f6..bc40141137 100644
--- a/compiler/gen_wasm/src/low_level.rs
+++ b/compiler/gen_wasm/src/low_level.rs
@@ -46,7 +46,14 @@ pub fn dispatch_low_level<'a>(
             return NotImplemented;
         }
         StrCountGraphemes => return BuiltinCall(bitcode::STR_COUNT_GRAPEHEME_CLUSTERS),
-        StrToNum => return NotImplemented, // choose builtin based on storage size
+        StrToNum => match ret_layout {
+            WasmLayout::Primitive(_, _) => return NotImplemented,
+            WasmLayout::StackMemory { size, .. } => {
+                // how do I decided Float vs. Int vs. Dec
+                // how do I find out if it's signed or unsigned
+                return BuiltinCall(bitcode::STR_TO_INT);
+            }
+        }, // choose builtin based on storage size
         StrFromInt => {
             // This does not get exposed in user space. We switched to NumToStr instead.
             // We can probably just leave this as NotImplemented. We may want remove this LowLevel.
diff --git a/compiler/test_gen/src/wasm_str.rs b/compiler/test_gen/src/wasm_str.rs
index cf4b1c1957..69a88fd2b1 100644
--- a/compiler/test_gen/src/wasm_str.rs
+++ b/compiler/test_gen/src/wasm_str.rs
@@ -1121,3 +1121,215 @@ fn str_trim_right_small_to_small_shared() {
         (RocStr, RocStr)
     );
 }
+
+#[test]
+fn str_to_nat() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toNat "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        usize
+    );
+}
+
+#[test]
+fn str_to_i128() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toI128 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        i128
+    );
+}
+
+#[test]
+fn str_to_u128() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toU128 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        u128
+    );
+}
+
+#[test]
+fn str_to_i64() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toI64 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        i64
+    );
+}
+
+#[test]
+fn str_to_u64() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toU64 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        u64
+    );
+}
+
+#[test]
+fn str_to_i32() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toI32 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        i32
+    );
+}
+
+#[test]
+fn str_to_u32() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toU32 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        u32
+    );
+}
+
+#[test]
+fn str_to_i16() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toI16 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        i16
+    );
+}
+
+#[test]
+fn str_to_u16() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toU16 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        u16
+    );
+}
+
+#[test]
+fn str_to_i8() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toI8 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        i8
+    );
+}
+
+#[test]
+fn str_to_u8() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toU8 "1" is
+                 Ok n -> n
+                 Err _ -> 0
+                "#
+        ),
+        1,
+        u8
+    );
+}
+
+#[test]
+fn str_to_f64() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toF64 "1.0" is
+                 Ok n -> n
+                 Err _ -> 0
+             "#
+        ),
+        1.0,
+        f64
+    );
+}
+
+#[test]
+fn str_to_f32() {
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toF32 "1.0" is
+                 Ok n -> n
+                 Err _ -> 0
+             "#
+        ),
+        1.0,
+        f32
+    );
+}
+
+#[test]
+fn str_to_dec() {
+    use roc_std::RocDec;
+
+    assert_evals_to!(
+        indoc!(
+            r#"
+             when Str.toDec "1.0" is
+                 Ok n -> n
+                 Err _ -> 0
+             "#
+        ),
+        RocDec::from_str("1.0").unwrap(),
+        RocDec
+    );
+}