diff --git a/examples/onnx_ptq/README.md b/examples/onnx_ptq/README.md
index 483dde359..012cbecf1 100644
--- a/examples/onnx_ptq/README.md
+++ b/examples/onnx_ptq/README.md
@@ -215,8 +215,7 @@ python -m modelopt.onnx.quantization \
     --quantize_mode=<int8/fp8> \
     --calibration_data=calib.npy \
     --calibrate_per_node \
-    --output_path=vit_base_patch16_224.quant.onnx \
-    --calibration_shapes=input:1x3x224x224
+    --output_path=vit_base_patch16_224.quant.onnx
 ```
 
 > **Note**: Per node calibration is not available for INT4 quantization methods (`awq_clip`, `rtn_dq`)
diff --git a/modelopt/onnx/quantization/fp8.py b/modelopt/onnx/quantization/fp8.py
index 1ef3c9799..ce7d56a26 100755
--- a/modelopt/onnx/quantization/fp8.py
+++ b/modelopt/onnx/quantization/fp8.py
@@ -164,7 +164,7 @@ def quantize(
     calibration_method: str = "entropy",
     calibration_data_reader: CalibrationDataReader = None,
     calibration_cache_path: str | None = None,
-    calibration_shapes: str | None = None,
+    calibration_shapes: str | dict | None = None,
     calibration_eps: list[str] = ["cpu", "cuda:0", "trt"],
     op_types_to_quantize: list[str] | None = None,
     op_types_to_exclude: list[str] | None = None,
diff --git a/modelopt/onnx/quantization/graph_utils.py b/modelopt/onnx/quantization/graph_utils.py
index 8a5b8ad57..6b37e3e7e 100755
--- a/modelopt/onnx/quantization/graph_utils.py
+++ b/modelopt/onnx/quantization/graph_utils.py
@@ -72,6 +72,15 @@ def has_const_input(node: Node) -> bool:
     return any(is_const_input(tensor) for tensor in node.inputs)
 
 
+def get_input_shapes(onnx_path: str) -> dict[str, list[int]]:
+    """Returns the input shapes of the given ONNX model."""
+    onnx_model = onnx.load(onnx_path)
+    input_shape_dict = {}
+    for input in onnx_model.graph.input:
+        input_shape_dict[input.name] = [x.dim_value for x in input.type.tensor_type.shape.dim]
+    return input_shape_dict
+
+
 def has_path_type(
     node: Node,
     graph: Graph,
@@ -923,7 +932,7 @@ def find_nodes_from_matmul_to_exclude(
     intermediate_generated_files: list[str] | None = None,
     calibration_data_reader: CalibrationDataReader = None,
     calibration_eps: list[str] = ["cpu", "cuda:0", "trt"],
-    calibration_shapes: str | None = None,
+    calibration_shapes: str | dict | None = None,
 ) -> list[str]:
     """Find MatMul nodes that meets gemv condition to exclude.
 
@@ -1050,7 +1059,7 @@ def find_nodes_from_convs_to_exclude(graph: Graph, quantize_mode: str = "int8"):
 
 
 def _exclude_matmuls_by_symbolic_inference(
-    model: onnx.ModelProto, matmul_nodes: list, calibration_shapes: str | None = None
+    model: onnx.ModelProto, matmul_nodes: list, calibration_shapes: str | dict | None = None
 ) -> list[str]:
     """Use symbolic shape inference to find MatMuls with dimension 1."""
     # Prepare model for symbolic inference
@@ -1061,7 +1070,11 @@ def _exclude_matmuls_by_symbolic_inference(
                 dim.dim_value = 1
 
     # Apply calibration shapes if provided
-    input_shapes = parse_shapes_spec(calibration_shapes) if calibration_shapes else {}
+    input_shapes = (
+        parse_shapes_spec(calibration_shapes)
+        if (calibration_shapes and isinstance(calibration_shapes, str))
+        else {}
+    )
     for graph_input in model.graph.input:
         if graph_input.name in input_shapes:
             input_shape = input_shapes[graph_input.name]
diff --git a/modelopt/onnx/quantization/int8.py b/modelopt/onnx/quantization/int8.py
index 5a878fb76..baf5a4383 100755
--- a/modelopt/onnx/quantization/int8.py
+++ b/modelopt/onnx/quantization/int8.py
@@ -115,7 +115,7 @@ def quantize(
     calibration_method: str = "entropy",
     calibration_data_reader: CalibrationDataReader = None,
     calibration_cache_path: str | None = None,
-    calibration_shapes: str | None = None,
+    calibration_shapes: str | dict | None = None,
     calibration_eps: list[str] = ["cpu", "cuda:0", "trt"],
     op_types_to_quantize: list[str] | None = None,
     op_types_to_exclude: list[str] | None = None,
diff --git a/modelopt/onnx/quantization/quantize.py b/modelopt/onnx/quantization/quantize.py
index daf785326..2d23b875a 100755
--- a/modelopt/onnx/quantization/quantize.py
+++ b/modelopt/onnx/quantization/quantize.py
@@ -53,6 +53,7 @@
 from modelopt.onnx.quantization.graph_utils import (
     cast_custom_ops,
     find_nodes_from_mha_to_exclude,
+    get_input_shapes,
     print_stat,
     remove_redundant_cast_nodes,
     validate_op_types_spelling,
@@ -255,6 +256,8 @@ def quantize(
             Path to pre-calculated activation tensor ranges, also known as calibration cache.
         calibration_shapes:
             Input shapes used for calibration process.
+            It should be provided as a string representing the shape of each input tensors for one calibration step.
+            Example input shapes spec: input0:1x3x256x256,input1:1x3x128x128
         calibration_eps:
             Priority order for the execution providers (EP) to calibrate the model.
             Any subset of ['NvTensorRtRtx', 'trt', 'cuda:x', 'dml:x', 'cpu'], where 'x' is the device id.
@@ -467,6 +470,9 @@ def quantize(
         calibration_eps,
     )
 
+    if not calibration_shapes:
+        calibration_shapes = get_input_shapes(onnx_path)
+
     if quantize_mode in ["fp8", "int8"]:
         quantize_func = quantize_int8 if quantize_mode == "int8" else quantize_fp8
         onnx_model = quantize_func(
diff --git a/modelopt/onnx/trt_utils.py b/modelopt/onnx/trt_utils.py
index 2231ccd00..e5a5d9a4a 100644
--- a/modelopt/onnx/trt_utils.py
+++ b/modelopt/onnx/trt_utils.py
@@ -266,6 +266,9 @@ def load_onnx_model(
     custom_ops = []
     has_custom_op = False
 
+    # Infer shapes
+    onnx.shape_inference.infer_shapes_path(onnx_path)
+
     # Load the model and weights
     onnx_model = onnx.load(onnx_path, load_external_data=True)
     size_threshold = 2 * (1024**3)  # 2GB