diff --git a/encoding.c b/encoding.c
index e377b5dab1b050..a49f3b6b3adc0f 100644
--- a/encoding.c
+++ b/encoding.c
@@ -1944,10 +1944,10 @@ static VALUE
 rb_enc_aliases(VALUE klass)
 {
     VALUE aliases[2];
-    aliases[0] = rb_hash_new();
     aliases[1] = rb_ary_new();
 
     GLOBAL_ENC_TABLE_LOCKING(enc_table) {
+        aliases[0] = rb_hash_new_capa(st_table_size(enc_table->names));
         st_foreach(enc_table->names, rb_enc_aliases_enc_i, (st_data_t)aliases);
     }
 
diff --git a/error.c b/error.c
index 7fc45b7225e3d7..923249ebe56fab 100644
--- a/error.c
+++ b/error.c
@@ -366,7 +366,7 @@ rb_warn_category(VALUE str, VALUE category)
     else {
         VALUE args[2];
         args[0] = str;
-        args[1] = rb_hash_new();
+        args[1] = rb_hash_new_capa(1);
         rb_hash_aset(args[1], sym_category, category);
         return rb_funcallv_kw(rb_mWarning, id_warn, 2, args, RB_PASS_KEYWORDS);
     }
@@ -1734,7 +1734,7 @@ exc_full_message(int argc, VALUE *argv, VALUE exc)
     order = check_order_keyword(opt);
 
     {
-        if (NIL_P(opt)) opt = rb_hash_new();
+        if (NIL_P(opt)) opt = rb_hash_new_capa(1);
         rb_hash_aset(opt, sym_highlight, highlight);
     }
 
diff --git a/eval_error.c b/eval_error.c
index f7a69c070ecb75..373f0d14074f0f 100644
--- a/eval_error.c
+++ b/eval_error.c
@@ -378,7 +378,7 @@ rb_ec_error_print_detailed0(rb_execution_context_t *const ec, const VALUE errinf
     volatile bool written = false;
     volatile VALUE emesg = emesg0;
 
-    volatile VALUE opt = rb_hash_new();
+    volatile VALUE opt = rb_hash_new_capa(1);
     volatile VALUE highlight = rb_stderr_tty_p() ? Qtrue : Qfalse;
     rb_hash_aset(opt, ID2SYM(rb_intern_const("highlight")), highlight);
 
diff --git a/gc.c b/gc.c
index 993ccdd5446224..d21019dbab24c7 100644
--- a/gc.c
+++ b/gc.c
@@ -2731,7 +2731,7 @@ count_objects(int argc, VALUE *argv, VALUE os)
     rb_gc_impl_each_object(rb_gc_get_objspace(), count_objects_i, &data);
 
     if (NIL_P(hash)) {
-        hash = rb_hash_new();
+        hash = rb_hash_new_capa(2 + T_MASK);
     }
     else if (!RHASH_EMPTY_P(hash)) {
         rb_hash_stlike_foreach(hash, set_zero, hash);
diff --git a/hash.c b/hash.c
index 57afe795a4b433..e8e97a80f80e75 100644
--- a/hash.c
+++ b/hash.c
@@ -1507,6 +1507,18 @@ hash_alloc_capa(VALUE klass, VALUE flags, VALUE ifnone, size_t size, bool frozen
     return hash;
 }
 
+static VALUE
+hash_hidden_new(size_t size)
+{
+    return hash_alloc_capa(0, 0, Qnil, size, false);
+}
+
+VALUE
+rb_hash_alloc_copy(VALUE klass, VALUE src)
+{
+    return hash_alloc_capa(klass, 0, Qnil, RHASH_SIZE(src), false);
+}
+
 static VALUE
 hash_alloc(VALUE klass)
 {
@@ -1530,12 +1542,6 @@ empty_hash_alloc(VALUE klass)
     return hash_alloc(klass);
 }
 
-VALUE
-rb_hash_new(void)
-{
-    return hash_alloc(rb_cHash);
-}
-
 static VALUE
 copy_compare_by_id(VALUE hash, VALUE basis)
 {
@@ -1551,6 +1557,12 @@ rb_hash_new_capa(long capa)
     return hash_alloc_capa(rb_cHash, 0, Qnil, capa, false);
 }
 
+VALUE
+rb_hash_new(void)
+{
+    return rb_hash_new_capa(0);
+}
+
 VALUE
 rb_hash_alloc_fixed_size(VALUE klass, st_index_t size)
 {
@@ -2714,7 +2726,7 @@ rb_hash_slice(int argc, VALUE *argv, VALUE hash)
     VALUE key, value, result;
 
     if (argc == 0 || RHASH_EMPTY_P(hash)) {
-        return copy_compare_by_id(rb_hash_new(), hash);
+        return copy_compare_by_id(rb_hash_new_capa(0), hash);
     }
     result = copy_compare_by_id(rb_hash_new_capa(argc), hash);
 
@@ -3378,7 +3390,7 @@ rb_hash_transform_keys(int argc, VALUE *argv, VALUE hash)
     else {
         RETURN_SIZED_ENUMERATOR(hash, 0, 0, hash_enum_size);
     }
-    result = rb_hash_new();
+    result = rb_hash_new_capa(RHASH_SIZE(hash));
     if (!RHASH_EMPTY_P(hash)) {
         if (transarg.trans) {
             transarg.result = result;
@@ -3505,7 +3517,7 @@ rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
     rb_hash_modify_check(hash);
     if (!RHASH_TABLE_EMPTY_P(hash)) {
         long i;
-        VALUE new_keys = hash_alloc(0);
+        VALUE new_keys = hash_hidden_new(RHASH_SIZE(hash));
         VALUE pairs = rb_ary_hidden_new(RHASH_SIZE(hash) * 2);
         rb_hash_foreach(hash, flatten_i, pairs);
         for (i = 0; i < RARRAY_LEN(pairs); i += 2) {
@@ -3531,7 +3543,6 @@ rb_hash_transform_keys_bang(int argc, VALUE *argv, VALUE hash)
             rb_hash_aset(new_keys, new_key, Qnil);
         }
         rb_ary_clear(pairs);
-        rb_hash_clear(new_keys);
     }
     compact_after_delete(hash);
     return hash;
@@ -4800,7 +4811,7 @@ rb_hash_compare_by_id_p(VALUE hash)
 VALUE
 rb_ident_hash_new(void)
 {
-    VALUE hash = rb_hash_new();
+    VALUE hash = rb_hash_new_capa(0);
     hash_st_table_init(hash, &identhash, 0);
     rb_gc_register_pinning_obj(hash);
     return hash;
@@ -4809,7 +4820,7 @@ rb_ident_hash_new(void)
 VALUE
 rb_ident_hash_new_capa(long size)
 {
-    VALUE hash = rb_hash_new();
+    VALUE hash = rb_hash_new_capa(0);
     hash_st_table_init(hash, &identhash, size);
     rb_gc_register_pinning_obj(hash);
     return hash;
@@ -6220,9 +6231,6 @@ env_slice(int argc, VALUE *argv, VALUE _)
     int i;
     VALUE key, value, result;
 
-    if (argc == 0) {
-        return rb_hash_new();
-    }
     result = rb_hash_new_capa(argc);
 
     for (i = 0; i < argc; i++) {
@@ -6607,14 +6615,26 @@ env_key(VALUE dmy, VALUE value)
     return str;
 }
 
+static inline size_t
+environ_size(char **env)
+{
+    size_t size = 0;
+    while (*env) {
+        size += 1;
+        env++;
+    }
+    return size;
+}
+
 static VALUE
 env_to_hash(void)
 {
-    VALUE hash = rb_hash_new();
+    VALUE hash;
 
     rb_encoding *enc = env_encoding();
     ENV_LOCKING() {
         char **env = GET_ENVIRON(environ);
+        hash = rb_hash_new_capa(environ_size(env));
         while (*env) {
             char *s = strchr(*env, '=');
             if (s) {
diff --git a/insns.def b/insns.def
index 3ad378081a4cac..553d1e4b242b06 100644
--- a/insns.def
+++ b/insns.def
@@ -592,7 +592,7 @@ newhash
         val = rb_hash_new_with_bulk_insert(num, STACK_ADDR_FROM_TOP(num));
     }
     else {
-        val = rb_hash_new();
+        val = rb_hash_new_capa(0);
     }
 }
 
diff --git a/object.c b/object.c
index bd53644a1c37a6..27b8654a7383ad 100644
--- a/object.c
+++ b/object.c
@@ -26,6 +26,7 @@
 #include "internal/class.h"
 #include "internal/error.h"
 #include "internal/eval.h"
+#include "internal/hash.h"
 #include "internal/inits.h"
 #include "internal/numeric.h"
 #include "internal/object.h"
@@ -484,7 +485,7 @@ clone_freeze_kwarg_hash(VALUE *cache, VALUE freeze_value)
 {
     VALUE h = RUBY_ATOMIC_VALUE_LOAD(*cache);
     if (!h) {
-        h = rb_hash_new();
+        h = rb_hash_alloc_fixed_size(rb_cHash, 1);
         rb_hash_aset(h, ID2SYM(idFreeze), freeze_value);
         rb_obj_freeze(h);
         rb_vm_register_global_object(h); /* pin before publishing */
@@ -1461,7 +1462,7 @@ nil_to_a(VALUE obj)
 static VALUE
 nil_to_h(VALUE obj)
 {
-    return rb_hash_new();
+    return rb_hash_new_capa(0);
 }
 
 /*
@@ -4023,11 +4024,11 @@ rb_Hash(VALUE val)
 {
     VALUE tmp;
 
-    if (NIL_P(val)) return rb_hash_new();
+    if (NIL_P(val)) return rb_hash_new_capa(0);
     tmp = rb_check_hash_type(val);
     if (NIL_P(tmp)) {
         if (RB_TYPE_P(val, T_ARRAY) && RARRAY_LEN(val) == 0)
-            return rb_hash_new();
+            return rb_hash_new_capa(0);
         rb_cant_convert(val, "Hash");
     }
     return tmp;