diff --git a/returnn/tf/layers/basic.py b/returnn/tf/layers/basic.py
index 1fa5726f6..691c89a64 100644
--- a/returnn/tf/layers/basic.py
+++ b/returnn/tf/layers/basic.py
@@ -7556,7 +7556,7 @@ class ResizeLayer(_ConcatInputLayer):
 
   def __init__(self, factor, axis, out_dim=None, kind="nn", fill_value=None, fill_dropout=None, **kwargs):
     """
-    :param int factor:
+    :param int|float|LayerBase factor: out_len = in_len * factor
     :param Dim|str axis: the axis to resize
     :param Dim|None out_dim:
     :param str kind: "linear", "nn"/"nearest_neighbor", "cubic", "fill"
@@ -7565,6 +7565,7 @@ def __init__(self, factor, axis, out_dim=None, kind="nn", fill_value=None, fill_
     """
     out_dim  # noqa  # via get_out_data_from_opts
     super(ResizeLayer, self).__init__(**kwargs)
+    self.factor = factor
     # self.output.shape and self.output.batch_dim_axis are already set here via self.get_out_data_from_opts().
     input_data = self.input_data.copy_as_batch_major()
     axis = input_data.get_axis_from_description(axis)
@@ -7580,7 +7581,20 @@ def __init__(self, factor, axis, out_dim=None, kind="nn", fill_value=None, fill_
     remaining_shape = [shape[i] for i in remaining_axes]
     remaining_dim = optional_mul(*remaining_shape) if remaining_axes else 1
     x = tf.reshape(x, [shape[0], shape[axis], 1, remaining_dim])  # [batch,height,width,channels]
-    new_size = shape[axis] * factor
+    if isinstance(factor, (int, float)):
+      factor_t = factor
+    elif isinstance(factor, LayerBase):
+      assert factor.output.batch_shape == (), "%s: factor must be scalar, got %s" % (self, factor)
+      assert factor.output.dtype in ("int32", "float32"), "%s: factor must be int or float, got %s" % (self, factor)
+      factor_t = factor.output.placeholder
+    else:
+      raise TypeError("%s: unexpected factor type %s" % (self, type(factor).__name__))
+    if isinstance(factor_t, int) or (isinstance(factor_t, tf.Tensor) and factor_t.dtype == tf.int32):
+      new_size = shape[axis] * factor_t
+    elif isinstance(factor_t, float) or (isinstance(factor_t, tf.Tensor) and factor_t.dtype == tf.float32):
+      new_size = tf.cast(tf.math.ceil(tf.cast(shape[axis], tf.float32) * factor_t), tf.int32)
+    else:
+      raise TypeError("%s: unexpected factor_t %s" % (self, factor_t))
     if kind == "linear":
       x = tf_compat.v1.image.resize_bilinear(x, size=(new_size, 1))
     elif kind == "cubic":
@@ -7605,6 +7619,7 @@ def __init__(self, factor, axis, out_dim=None, kind="nn", fill_value=None, fill_
       raise Exception("invalid kind %r for resizing" % kind)
     x = tf.reshape(x, [shape[0], new_size] + remaining_shape)  # [batch,new_size] + remaining_shape
     if fill_dropout:
+      assert isinstance(factor, int)
       from returnn.tf.util.basic import expand_dims_unbroadcast
       # We are going to build a mask over the axis. This mask will be shared over all seqs in the batch.
       # Similar to in tf.nn.dropout. Build random_tensor as uniform [keep_prob, 1.0 + keep_prob).
@@ -7626,12 +7641,44 @@ def __init__(self, factor, axis, out_dim=None, kind="nn", fill_value=None, fill_
           out_dyn_size, maxlen=new_size, dtype=tf.bool)  # (batch,new_size)
         out_dyn_size = tf.reduce_sum(tf.cast(tf.logical_and(mask, orig_mask), tf.int32), axis=1)
         self.output.dim_tags[axis].dyn_size = out_dyn_size
+    elif not isinstance(factor, int):
+      dyn_size_ext = input_data.dim_tags[axis].dyn_size_ext
+      if dyn_size_ext is not None and dyn_size_ext.placeholder is not None:
+        dyn_size_ext = dyn_size_ext.copy(name="%s:dyn_size_ext" % self.name)
+        if isinstance(factor_t, int) or (isinstance(factor_t, tf.Tensor) and factor_t.dtype == tf.int32):
+          dyn_size_ext.placeholder = dyn_size_ext.placeholder * factor_t
+        elif isinstance(factor_t, float) or (isinstance(factor_t, tf.Tensor) and factor_t.dtype == tf.float32):
+          dyn_size_ext.placeholder = tf.cast(
+            tf.math.ceil(tf.cast(dyn_size_ext.placeholder, tf.float32) * factor_t), tf.int32)
+        else:
+          raise TypeError("%s: unexpected factor_t %s" % (self, factor_t))
+        self.output.dim_tags[axis].dyn_size_ext = dyn_size_ext
     self.output.placeholder = x
 
+  def get_dep_layers(self):
+    """
+    :rtype: list[LayerBase]
+    """
+    deps = super(ResizeLayer, self).get_dep_layers()
+    if isinstance(self.factor, LayerBase):
+      deps.append(self.factor)
+    return deps
+
+  @classmethod
+  def transform_config_dict(cls, d, network, get_layer):
+    """
+    :param dict[str] d:
+    :param returnn.tf.network.TFNetwork network:
+    :param (str)->LayerBase get_layer:
+    """
+    super(ResizeLayer, cls).transform_config_dict(d, network=network, get_layer=get_layer)
+    if isinstance(d.get("factor"), str):
+      d["factor"] = get_layer(d["factor"])
+
   @classmethod
   def get_out_data_from_opts(cls, factor, axis, sources, name, fill_dropout=None, out_dim=None, **kwargs):
     """
-    :param int factor:
+    :param int|float|LayerBase factor:
     :param Dim|str axis:
     :param list[LayerBase] sources:
     :param str name:
@@ -7646,8 +7693,10 @@ def get_out_data_from_opts(cls, factor, axis, sources, name, fill_dropout=None,
     axis = 1
     assert axis != out.batch_dim_axis, "batch-dim resize not supported"
     tag = out.dim_tags[axis]
-    if fill_dropout:
+    if fill_dropout or not isinstance(factor, int):
       out_dim_ = Dim(kind=tag.kind, description="%s_resize" % name, auto_generated=True)  # unknown dim
+      if tag.dyn_size_ext is not None:
+        out_dim_.dyn_size_ext = tag.dyn_size_ext.copy_template(name="%s:dyn_size_ext" % name)
     else:
       out_dim_ = tag * factor
     if out_dim:
diff --git a/tests/test_TFNetworkLayer.py b/tests/test_TFNetworkLayer.py
index 39cf3b1f9..7f671aa48 100644
--- a/tests/test_TFNetworkLayer.py
+++ b/tests/test_TFNetworkLayer.py
@@ -8047,6 +8047,35 @@ def test_ResizeLayer_BFT():
     assert out_v.shape == (n_batch, n_in, n_time * 2)
 
 
+def test_ResizeLayer_dynamic():
+  n_batch, n_time, n_in = 2, 5, 3
+  in_v = numpy.arange(0, n_batch * n_time * n_in).astype("float32").reshape((n_batch, n_time, n_in))
+  in_seq_lens = numpy.array([5, 4])
+  config = Config({
+    "extern_data": {
+      "data": {"shape": (None, n_in)},
+      "factor": {"shape": (), "batch_dim_axis": None, "dtype": "float32"},
+    }
+  })
+  with make_scope() as session:
+    net = TFNetwork(config=config)
+    net.construct_from_dict({
+      "output": {"class": "resize", "axis": "T", "factor": "data:factor", "kind": "nn", "from": "data"}
+    })
+    out = net.get_default_output_layer().output
+    for factor in [0.5, 2.0]:
+      out_v, out_lens = session.run(
+        (out.placeholder, out.get_sequence_lengths()), feed_dict={
+          net.extern_data.get_batch_info().dim: n_batch,
+          net.extern_data.data["data"].placeholder: in_v,
+          net.extern_data.data["data"].get_sequence_lengths(): in_seq_lens,
+          net.extern_data.data["factor"].placeholder: factor,
+        })
+      assert isinstance(out_v, numpy.ndarray)
+      assert out_v.shape == (n_batch, numpy.ceil(n_time * factor), n_in)
+      numpy.testing.assert_equal(out_lens, numpy.ceil(in_seq_lens * factor).astype("int32"))
+
+
 def test_PostfixInTimeLayer():
   with make_scope() as session:
     import numpy as np