diff --git a/auto_tune_vllm/cli/main.py b/auto_tune_vllm/cli/main.py
index cbc5d23..0935ea0 100644
--- a/auto_tune_vllm/cli/main.py
+++ b/auto_tune_vllm/cli/main.py
@@ -18,6 +18,7 @@
 from ..core.study_controller import StudyController
 from ..execution.backends import RayExecutionBackend
 from ..logging.manager import CentralizedLogger, LogStreamer
+from ..utils.grid_cardinality import get_parameter_grid_cardinality
 
 # Setup rich console and app
 console = Console()
@@ -369,7 +370,40 @@ def run_optimization_sync(
     create_db: bool = False,
 ):
     """Synchronous optimization runner with progress display."""
-    # Create study controller
+    total_trials = n_trials or config.optimization.n_trials
+    cardinality = get_parameter_grid_cardinality(config)
+    if total_trials >= cardinality:
+        requested = total_trials
+        config.optimization.sampler = "grid"
+        config.optimization.n_trials = cardinality
+        config.optimization.n_startup_trials = min(
+            config.optimization.n_startup_trials, max(0, cardinality - 1)
+        )
+        n_trials = cardinality
+        total_trials = cardinality
+        console.print(
+            f"[yellow]n_trials ({requested}) meets or exceeds grid cardinality "
+            f"({cardinality}). "
+            "Search set to grid mode with n_trials = cardinality.[/yellow]"
+        )
+    elif (
+        config.optimization.sampler.lower() in ("tpe", "gp", "botorch")
+        and total_trials <= config.optimization.n_startup_trials
+    ):
+        startup_before = config.optimization.n_startup_trials
+        prev_sampler = config.optimization.sampler
+        config.optimization.sampler = "random"
+        config.optimization.n_trials = total_trials
+        config.optimization.n_startup_trials = min(
+            startup_before, max(0, total_trials - 1)
+        )
+        console.print(
+            f"[yellow]Auto-switched sampler from '{prev_sampler}' to 'random': "
+            f"n_trials ({total_trials}) is <= n_startup_trials ({startup_before}), "
+            "so startup sampling would consume the full trial budget. "
+            f"n_startup_trials is now {config.optimization.n_startup_trials}.[/yellow]"
+        )
+    # Create study controller (uses config with possibly updated sampler/n_trials)
     controller = StudyController.create_from_config(
         backend, config, create_db=create_db
     )
@@ -381,8 +415,6 @@ def run_optimization_sync(
     _display_log_viewing_instructions(config)
     console.print()  # Add blank line for better readability
 
-    total_trials = n_trials or config.optimization.n_trials
-
     with Progress(
         SpinnerColumn(),
         TextColumn("[progress.description]{task.description}"),
@@ -1086,6 +1118,11 @@ def validate_command(
             "Optimization", f"{opt_summary} ({study_config.optimization.sampler})"
         )
         table.add_row("Trials", str(study_config.optimization.n_trials))
+        cardinality = get_parameter_grid_cardinality(study_config)
+        table.add_row(
+            "Possible combinations (grid cardinality)",
+            str(cardinality),
+        )
         table.add_row("Model", study_config.benchmark.model)
         table.add_row(
             "Parameters",
diff --git a/auto_tune_vllm/utils/__init__.py b/auto_tune_vllm/utils/__init__.py
index 7a5a58f..3d2a3ca 100644
--- a/auto_tune_vllm/utils/__init__.py
+++ b/auto_tune_vllm/utils/__init__.py
@@ -2,6 +2,7 @@
 Utilities for auto-tune-vllm package.
 """
 
+from .grid_cardinality import get_parameter_grid_cardinality
 from .version_manager import VLLMDefaultsVersion, VLLMVersionManager
 from .vllm_cli_parser import ArgumentType, CLIArgument, VLLMCLIParser
 
@@ -11,4 +12,5 @@
     "ArgumentType",
     "VLLMVersionManager",
     "VLLMDefaultsVersion",
+    "get_parameter_grid_cardinality",
 ]
diff --git a/auto_tune_vllm/utils/grid_cardinality.py b/auto_tune_vllm/utils/grid_cardinality.py
new file mode 100644
index 0000000..1f829d0
--- /dev/null
+++ b/auto_tune_vllm/utils/grid_cardinality.py
@@ -0,0 +1,61 @@
+"""
+Compute the total cardinality of the parameter grid from a study config.
+Uses the same logic as StudyController._create_search_space for consistency.
+"""
+
+from pathlib import Path
+from typing import Union
+
+from auto_tune_vllm.core.config import StudyConfig
+from auto_tune_vllm.core.parameters import (
+    BooleanParameter,
+    EnvironmentParameter,
+    ListParameter,
+    ParameterConfig,
+    RangeParameter,
+)
+
+_MAX_GRID_SIZE = 10000
+
+
+def _count_parameter_values(param: ParameterConfig) -> int:
+    """Count distinct values for one parameter (mirrors _create_search_space)."""
+    if isinstance(param, (ListParameter, EnvironmentParameter)):
+        return len(param.options)
+    if isinstance(param, RangeParameter):
+        min_val = param.min_value
+        max_val = param.max_value
+        if param.data_type is float:
+            step = param.step
+            if step is None:
+                return _MAX_GRID_SIZE
+            n_steps = int(round((max_val - min_val) / step)) + 1
+            return min(n_steps, _MAX_GRID_SIZE)
+        step = param.step or 1
+        current = min_val
+        count = 0
+        while current <= max_val and count < _MAX_GRID_SIZE:
+            count += 1
+            current += step
+        return count
+    if isinstance(param, BooleanParameter):
+        return 2
+    raise ValueError(f"Unknown parameter type: {type(param)}")
+
+
+def get_parameter_grid_cardinality(
+    config: Union[str, Path, StudyConfig],
+    vllm_version: str | None = None,
+) -> int:
+    """
+    Return the total number of points in the parameter grid (product of enabled params).
+
+    config: Path to YAML, or an already-loaded StudyConfig.
+    """
+    if isinstance(config, (str, Path)):
+        config = StudyConfig.from_file(str(config), vllm_version=vllm_version)
+    total = 1
+    for param_config in config.parameters.values():
+        if param_config.enabled:
+            total *= _count_parameter_values(param_config)
+    return total