diff --git a/estimation.py b/estimation.py
new file mode 100644
index 000000000..70bd3e601
--- /dev/null
+++ b/estimation.py
@@ -0,0 +1,212 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.
+
+import contextlib
+import gc
+import os
+
+import torch
+import torch.nn.functional as F
+from torch._guards import active_fake_mode
+from torch._subclasses.fake_tensor import FakeTensorMode
+from torch.distributed import destroy_process_group
+from torch.distributed._tools.fsdp2_mem_tracker import FSDPMemTracker
+from torch.distributed.tensor.parallel import loss_parallel
+from torch.testing._internal.distributed.fake_pg import FakeStore
+
+from torchtitan.config_manager import JobConfig
+from torchtitan.datasets import create_tokenizer
+from torchtitan.float8_linear import build_fp8_linear
+from torchtitan.logging_utils import init_logger, logger
+from torchtitan.lr_scheduling import get_lr_schedulers
+from torchtitan.models import model_name_to_cls, model_name_to_tokenizer, models_config
+from torchtitan.parallelisms import models_parallelize_fns, ParallelDims
+from train import build_optimizers
+
+
+def estimate_memory(job_config: JobConfig):
+    init_logger()
+    logger.info("Estimating memory usage...")
+    gc.disable()
+    gc.collect(1)
+
+    # Get the world size
+    world_size = int(os.environ["WORLD_SIZE"])
+
+    # if tp > or pp > 1, we exit
+    if (
+        job_config.training.tensor_parallel_degree > 1
+        or job_config.experimental.pipeline_parallel_degree > 1
+    ):
+        logger.info(
+            "Tensor parallelism and pipeline parallelism are not supported yet."
+        )
+        return
+
+    # fake tensor doesn't work with fused rmsnorm
+    if (
+        job_config.model.norm_type == "fused_rmsnorm"
+        and job_config.estimate.mode == "fake"
+    ):
+        logger.info(
+            "Fused RMSNorm is not supported yet under fake estimation mode. "
+            "Switching to rmsnorm."
+        )
+        job_config.model.norm_type = "rmsnorm"
+
+    parallel_dims = ParallelDims(
+        dp=job_config.training.data_parallel_degree,
+        tp=job_config.training.tensor_parallel_degree,
+        pp=job_config.experimental.pipeline_parallel_degree,
+        world_size=world_size,
+        enable_loss_parallel=job_config.training.enable_loss_parallel,
+    )
+
+    device = torch.device(f"cuda:{int(os.environ['LOCAL_RANK'])}")
+    torch.cuda.set_device(device)
+
+    # init fake pg
+    store = FakeStore()
+    torch.distributed.init_process_group(
+        "fake", rank=int(os.environ["LOCAL_RANK"]), world_size=world_size, store=store
+    )
+
+    # build meshes
+    world_mesh = parallel_dims.build_mesh(device_type="cuda")
+
+    if not parallel_dims.dp_enabled:
+        logger.info("Data parallelism is not enabled. Skipping memory estimation.")
+        return
+
+    model_name = job_config.model.name
+
+    # build tokenizer
+    tokenizer_type = model_name_to_tokenizer[model_name]
+    tokenizer = create_tokenizer(tokenizer_type, job_config.model.tokenizer_path)
+
+    # loss_parallel enables dispatching to efficient loss operators
+    loss_parallel_ctx = (
+        loss_parallel if parallel_dims.loss_parallel_enabled else contextlib.nullcontext
+    )
+
+    # loss fn can be shared by pipeline-parallel or non-pp execution
+    def loss_fn(pred, labels):
+        return F.cross_entropy(pred.flatten(0, 1), labels.flatten(0, 1))
+
+    # build model (using meta init)
+    model_cls = model_name_to_cls[model_name]
+    model_config = models_config[model_name][job_config.model.flavor]
+    # set the model configs from training inputs:
+    # 1. norm type to decide which norm layer to use
+    # 2. vocab size from tokenizer
+    # 3. max_seq_len base on inputs
+    model_config.norm_type = job_config.model.norm_type
+    model_config.vocab_size = tokenizer.n_words
+    model_config.max_seq_len = job_config.training.seq_len
+
+    with FakeTensorMode() if job_config.estimate.mode == "fake" else contextlib.nullcontext():
+
+        logger.info(
+            f"Building {model_name} {job_config.model.flavor} with {model_config}"
+        )
+        with torch.device("meta"):
+            whole_model = model_cls.from_model_args(model_config)
+
+        # apply fp8 linear module swap
+        if job_config.training.fp8_linear:
+            build_fp8_linear(whole_model, job_config)
+
+        # apply PT-D DP/TP parallelisms and activation checkpointing
+        model_parts = [whole_model]
+        model_parts = [
+            models_parallelize_fns[model_name](m, world_mesh, parallel_dims, job_config)
+            for m in model_parts
+        ]
+
+        init_device = "cuda"
+        for model in model_parts:
+            model.to_empty(device=init_device)
+
+        if not active_fake_mode():
+            whole_model.init_weights()
+
+        # build optimizer after applying parallelisms to the model
+        optimizers = build_optimizers(model_parts, job_config)
+        lr_schedulers = get_lr_schedulers(optimizers.optimizers, job_config)
+
+        for model in model_parts:
+            model.train()
+        logger.info(f"Vocab size: {model_config.vocab_size}")
+        # Create a dummy batch instead of loading from a dataset
+        batch = (
+            torch.randint(
+                0,
+                model_config.vocab_size,
+                (job_config.training.batch_size, model_config.max_seq_len),
+                device="cuda",
+            ),
+            torch.randint(
+                0,
+                model_config.vocab_size,
+                (job_config.training.batch_size, model_config.max_seq_len),
+                device="cuda",
+            ),
+        )
+        fsdp_memtracker = FSDPMemTracker(mod=whole_model, optm=optimizers.optimizers[0])
+        fsdp_memtracker.track_inputs(batch)
+
+        with fsdp_memtracker:
+            for iter_idx in range(2):
+                input_ids, labels = batch
+                # train step
+                with loss_parallel_ctx():
+                    pred = whole_model(input_ids)
+                    loss = loss_fn(pred, labels)
+                    del pred
+                    loss.backward()
+
+                # clip gradients
+                for model in model_parts:
+                    torch.nn.utils.clip_grad_norm_(
+                        model.parameters(), job_config.training.max_norm, foreach=True
+                    )
+                # optimizer step
+                optimizers.step()
+                lr_schedulers.step()
+                optimizers.zero_grad()
+                print(f"Peak Memory at iter: {iter_idx}")
+                fsdp_memtracker.display_snapshot("peak", units="MiB", tabulate=True)
+                if iter_idx == 0:
+                    fsdp_memtracker.reset_mod_stats()  # iter 0 does not have optimizer state
+                gc.collect(1)
+
+        fsdp_memtracker.display_modulewise_snapshots(
+            depth=3, units="MiB", tabulate=True
+        )
+        mem_stats = torch.cuda.memory_stats()
+        peak_active = mem_stats["active_bytes.all.peak"]
+        peak_reserved = mem_stats["reserved_bytes.all.peak"]
+        num_retries = mem_stats["num_alloc_retries"]
+        dev = torch.device(torch.cuda.current_device())
+        tracker_peak = fsdp_memtracker.get_tracker_snapshot("peak")[dev]["Total"]
+        gib = 1024**3
+        print(
+            f"peak active: {peak_active / gib} GiB | peak reserved:"
+            f" {peak_reserved / gib} GiB | num_retries: {num_retries}"
+        )
+        print(f"Tracker Max: {tracker_peak / gib} GiB")
+        if job_config.estimate.mode == "real":
+            print(f"Tracker Accuracy: {tracker_peak/peak_active}")
+        gc.enable()
+
+
+if __name__ == "__main__":
+    config = JobConfig()
+    config.parse_args()
+    try:
+        estimate_memory(config)
+    finally:
+        destroy_process_group()
diff --git a/run_llama_train.sh b/run_llama_train.sh
index 33aaf79b5..ca2001a8d 100755
--- a/run_llama_train.sh
+++ b/run_llama_train.sh
@@ -10,13 +10,14 @@ set -ex
 # libUV is a scalable backend for TCPStore which is used in processGroup
 # rendezvous. This is the recommended backend for distributed training.
 export USE_LIBUV=1
-TRAINER_DIR=${1:-/home/$USER/local/torchtitan}
+TRAINER_DIR=${TRAINER_DIR:-/home/$USER/local/torchtitan}
 
 # use envs as local overrides for convenience
 # e.g.
 # LOG_RANK=0,1 NGPU=4 ./run_llama_train.sh
 
 NGPU=${NGPU:-"8"}
+NNODES=${NNODES:-"1"}
 
 # by default log just rank 0 output,
 LOG_RANK=${LOG_RANK:-0}
@@ -29,6 +30,16 @@ if [ $# -ne 0 ]; then
     overrides="$*"
 fi
 
-torchrun --nproc_per_node=${NGPU} --rdzv_backend c10d --rdzv_endpoint="localhost:0" \
---local-ranks-filter ${LOG_RANK} --role rank --tee 3 \
-train.py --job.config_file ${CONFIG_FILE} $overrides
+# Check if --estimate.memory=True is in the arguments
+if echo "$overrides" | grep -q -- "--estimate.memory=True"; then
+    # Calculate WORLD_SIZE as the product of NGPU and NNODES
+    # Export WORLD_SIZE and LOCAL_RANK
+    export WORLD_SIZE=$((NGPU * NNODES))
+    export LOCAL_RANK=0
+    python estimation.py --job.config_file ${CONFIG_FILE} $overrides
+else
+    # Call train.py if not in estimation mode
+    torchrun --nproc_per_node=${NGPU} --rdzv_backend c10d --rdzv_endpoint="localhost:0" \
+    --local-ranks-filter ${LOG_RANK} --role rank --tee 3 \
+    train.py --job.config_file ${CONFIG_FILE} $overrides
+fi
diff --git a/torchtitan/config_manager.py b/torchtitan/config_manager.py
index 6e06d93a9..2ff216e14 100644
--- a/torchtitan/config_manager.py
+++ b/torchtitan/config_manager.py
@@ -480,6 +480,20 @@ def __init__(self):
             help="Flight recorder ring buffer size, >0 means recording by default, 0 means disabled",
         )
 
+        # estimation mode settings
+        self.parser.add_argument(
+            "--estimate.memory",
+            help="Whether to estimate memory usage for FSDP",
+            default=False,
+        )
+
+        self.parser.add_argument(
+            "--estimate.mode",
+            type=str,
+            default="fake",
+            help="Mode of estimation to use ['fake', 'real']",
+        )
+
     def parse_args(self, args_list: list = sys.argv[1:]):
         args, cmd_args = self.parse_args_from_command_line(args_list)
         config_file = getattr(args, "job.config_file", None)