diff --git a/pandas/_libs/tslibs/dtypes.pxd b/pandas/_libs/tslibs/dtypes.pxd
index 356bd9dc3d7a0..6e41a55f30929 100644
--- a/pandas/_libs/tslibs/dtypes.pxd
+++ b/pandas/_libs/tslibs/dtypes.pxd
@@ -8,7 +8,6 @@ cdef NPY_DATETIMEUNIT abbrev_to_npy_unit(str abbrev)
 cdef NPY_DATETIMEUNIT freq_group_code_to_npy_unit(int freq) nogil
 cpdef int64_t periods_per_day(NPY_DATETIMEUNIT reso=*) except? -1
 cpdef int64_t periods_per_second(NPY_DATETIMEUNIT reso) except? -1
-cdef int64_t get_conversion_factor(NPY_DATETIMEUNIT from_unit, NPY_DATETIMEUNIT to_unit) except? -1
 
 cdef dict attrname_to_abbrevs
 
diff --git a/pandas/_libs/tslibs/dtypes.pyx b/pandas/_libs/tslibs/dtypes.pyx
index 01616666bba3f..a0a7ab90ebb30 100644
--- a/pandas/_libs/tslibs/dtypes.pyx
+++ b/pandas/_libs/tslibs/dtypes.pyx
@@ -4,7 +4,10 @@ cimport cython
 
 from enum import Enum
 
-from pandas._libs.tslibs.np_datetime cimport NPY_DATETIMEUNIT
+from pandas._libs.tslibs.np_datetime cimport (
+    NPY_DATETIMEUNIT,
+    get_conversion_factor,
+)
 
 
 cdef class PeriodDtypeBase:
@@ -386,83 +389,11 @@ cpdef int64_t periods_per_day(NPY_DATETIMEUNIT reso=NPY_DATETIMEUNIT.NPY_FR_ns)
     """
     How many of the given time units fit into a single day?
     """
-    cdef:
-        int64_t day_units
-
-    if reso == NPY_DATETIMEUNIT.NPY_FR_ps:
-        # pico is the smallest unit for which we don't overflow, so
-        #  we exclude femto and atto
-        day_units = 24 * 3600 * 1_000_000_000_000
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_ns:
-        day_units = 24 * 3600 * 1_000_000_000
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_us:
-        day_units = 24 * 3600 * 1_000_000
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_ms:
-        day_units = 24 * 3600 * 1_000
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_s:
-        day_units = 24 * 3600
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_m:
-        day_units = 24 * 60
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_h:
-        day_units = 24
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_D:
-        day_units = 1
-    else:
-        raise NotImplementedError(reso)
-    return day_units
+    return get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_D, reso)
 
 
 cpdef int64_t periods_per_second(NPY_DATETIMEUNIT reso) except? -1:
-    if reso == NPY_DATETIMEUNIT.NPY_FR_ns:
-        return 1_000_000_000
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_us:
-        return 1_000_000
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_ms:
-        return 1_000
-    elif reso == NPY_DATETIMEUNIT.NPY_FR_s:
-        return 1
-    else:
-        raise NotImplementedError(reso)
-
-
-@cython.overflowcheck(True)
-cdef int64_t get_conversion_factor(NPY_DATETIMEUNIT from_unit, NPY_DATETIMEUNIT to_unit) except? -1:
-    """
-    Find the factor by which we need to multiply to convert from from_unit to to_unit.
-    """
-    if (
-        from_unit == NPY_DATETIMEUNIT.NPY_FR_GENERIC
-        or to_unit == NPY_DATETIMEUNIT.NPY_FR_GENERIC
-    ):
-        raise ValueError("unit-less resolutions are not supported")
-    if from_unit > to_unit:
-        raise ValueError
-
-    if from_unit == to_unit:
-        return 1
-
-    if from_unit == NPY_DATETIMEUNIT.NPY_FR_W:
-        return 7 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_D, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_D:
-        return 24 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_h, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_h:
-        return 60 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_m, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_m:
-        return 60 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_s, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_s:
-        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_ms, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_ms:
-        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_us, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_us:
-        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_ns, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_ns:
-        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_ps, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_ps:
-        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_fs, to_unit)
-    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_fs:
-        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_as, to_unit)
-    else:
-        raise ValueError(from_unit, to_unit)
+    return get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_s, reso)
 
 
 cdef dict _reso_str_map = {
diff --git a/pandas/_libs/tslibs/np_datetime.pxd b/pandas/_libs/tslibs/np_datetime.pxd
index 290483a741fe7..420d83909a78d 100644
--- a/pandas/_libs/tslibs/np_datetime.pxd
+++ b/pandas/_libs/tslibs/np_datetime.pxd
@@ -102,6 +102,7 @@ cpdef cnp.ndarray astype_overflowsafe(
     cnp.dtype dtype,  # ndarray[datetime64[anyunit]]
     bint copy=*,
 )
+cdef int64_t get_conversion_factor(NPY_DATETIMEUNIT from_unit, NPY_DATETIMEUNIT to_unit) except? -1
 
 cdef bint cmp_dtstructs(npy_datetimestruct* left, npy_datetimestruct* right, int op)
 cdef get_implementation_bounds(
diff --git a/pandas/_libs/tslibs/np_datetime.pyx b/pandas/_libs/tslibs/np_datetime.pyx
index 692b4430fa577..494eb5da7e107 100644
--- a/pandas/_libs/tslibs/np_datetime.pyx
+++ b/pandas/_libs/tslibs/np_datetime.pyx
@@ -1,3 +1,4 @@
+cimport cython
 from cpython.datetime cimport (
     PyDateTime_DATE_GET_HOUR,
     PyDateTime_DATE_GET_MICROSECOND,
@@ -450,3 +451,43 @@ cdef int op_to_op_code(op):
         return Py_GE
     if op is operator.gt:
         return Py_GT
+
+
+@cython.overflowcheck(True)
+cdef int64_t get_conversion_factor(NPY_DATETIMEUNIT from_unit, NPY_DATETIMEUNIT to_unit) except? -1:
+    """
+    Find the factor by which we need to multiply to convert from from_unit to to_unit.
+    """
+    if (
+        from_unit == NPY_DATETIMEUNIT.NPY_FR_GENERIC
+        or to_unit == NPY_DATETIMEUNIT.NPY_FR_GENERIC
+    ):
+        raise ValueError("unit-less resolutions are not supported")
+    if from_unit > to_unit:
+        raise ValueError
+
+    if from_unit == to_unit:
+        return 1
+
+    if from_unit == NPY_DATETIMEUNIT.NPY_FR_W:
+        return 7 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_D, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_D:
+        return 24 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_h, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_h:
+        return 60 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_m, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_m:
+        return 60 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_s, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_s:
+        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_ms, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_ms:
+        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_us, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_us:
+        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_ns, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_ns:
+        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_ps, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_ps:
+        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_fs, to_unit)
+    elif from_unit == NPY_DATETIMEUNIT.NPY_FR_fs:
+        return 1000 * get_conversion_factor(NPY_DATETIMEUNIT.NPY_FR_as, to_unit)
+    else:
+        raise ValueError(from_unit, to_unit)
diff --git a/pandas/_libs/tslibs/timedeltas.pyx b/pandas/_libs/tslibs/timedeltas.pyx
index fef2a317a4f26..c64a9fb4d9c36 100644
--- a/pandas/_libs/tslibs/timedeltas.pyx
+++ b/pandas/_libs/tslibs/timedeltas.pyx
@@ -35,10 +35,7 @@ from pandas._libs.tslibs.conversion cimport (
     cast_from_unit,
     precision_from_unit,
 )
-from pandas._libs.tslibs.dtypes cimport (
-    get_conversion_factor,
-    npy_unit_to_abbrev,
-)
+from pandas._libs.tslibs.dtypes cimport npy_unit_to_abbrev
 from pandas._libs.tslibs.nattype cimport (
     NPY_NAT,
     c_NaT as NaT,
@@ -50,6 +47,7 @@ from pandas._libs.tslibs.np_datetime cimport (
     NPY_FR_ns,
     cmp_dtstructs,
     cmp_scalar,
+    get_conversion_factor,
     get_datetime64_unit,
     get_timedelta64_value,
     get_unit_from_dtype,
diff --git a/pandas/_libs/tslibs/timestamps.pyx b/pandas/_libs/tslibs/timestamps.pyx
index ae3ce46cbc3c8..3cf9c9bcda538 100644
--- a/pandas/_libs/tslibs/timestamps.pyx
+++ b/pandas/_libs/tslibs/timestamps.pyx
@@ -54,7 +54,6 @@ from pandas._libs.tslibs.conversion cimport (
     maybe_localize_tso,
 )
 from pandas._libs.tslibs.dtypes cimport (
-    get_conversion_factor,
     npy_unit_to_abbrev,
     periods_per_day,
     periods_per_second,
@@ -83,6 +82,7 @@ from pandas._libs.tslibs.np_datetime cimport (
     NPY_FR_ns,
     cmp_dtstructs,
     cmp_scalar,
+    get_conversion_factor,
     get_datetime64_unit,
     get_datetime64_value,
     get_unit_from_dtype,