diff --git a/.changeset/tidy-baths-rule.md b/.changeset/tidy-baths-rule.md
new file mode 100644
index 000000000..a9a28b7b8
--- /dev/null
+++ b/.changeset/tidy-baths-rule.md
@@ -0,0 +1,5 @@
+---
+'@solana/kit': patch
+---
+
+Add loadedAccountsDataSize to simulateTransaction response
diff --git a/packages/errors/src/json-rpc-error.ts b/packages/errors/src/json-rpc-error.ts
index 0025049a8..17c9a9156 100644
--- a/packages/errors/src/json-rpc-error.ts
+++ b/packages/errors/src/json-rpc-error.ts
@@ -84,6 +84,7 @@ export interface RpcSimulateTransactionResult {
               )[];
           }[]
         | null;
+    loadedAccountsDataSize: number | null;
     logs: string[] | null;
     returnData: {
         data: [string, 'base64'];
diff --git a/packages/rpc-api/src/__tests__/send-transaction-test.ts b/packages/rpc-api/src/__tests__/send-transaction-test.ts
index 9c45a94cd..f8cbf25d8 100644
--- a/packages/rpc-api/src/__tests__/send-transaction-test.ts
+++ b/packages/rpc-api/src/__tests__/send-transaction-test.ts
@@ -248,6 +248,7 @@ describe('sendTransaction', () => {
                 accounts: null,
                 cause: new SolanaError(SOLANA_ERROR__TRANSACTION_ERROR__ACCOUNT_NOT_FOUND),
                 innerInstructions: null,
+                loadedAccountsDataSize: 0,
                 logs: [],
                 returnData: null,
                 unitsConsumed: 0,
@@ -283,6 +284,7 @@ describe('sendTransaction', () => {
                 accounts: null,
                 cause: new SolanaError(SOLANA_ERROR__TRANSACTION_ERROR__INSUFFICIENT_FUNDS_FOR_FEE),
                 innerInstructions: null,
+                loadedAccountsDataSize: 0,
                 logs: [],
                 returnData: null,
                 unitsConsumed: 0,
@@ -315,6 +317,7 @@ describe('sendTransaction', () => {
                 accounts: null,
                 cause: new SolanaError(SOLANA_ERROR__TRANSACTION_ERROR__BLOCKHASH_NOT_FOUND),
                 innerInstructions: null,
+                loadedAccountsDataSize: 0,
                 logs: [],
                 returnData: null,
                 unitsConsumed: 0,
diff --git a/packages/rpc-api/src/__tests__/simulate-transaction-test.ts b/packages/rpc-api/src/__tests__/simulate-transaction-test.ts
index 33646da55..272ce80f0 100644
--- a/packages/rpc-api/src/__tests__/simulate-transaction-test.ts
+++ b/packages/rpc-api/src/__tests__/simulate-transaction-test.ts
@@ -173,6 +173,7 @@ describe('simulateTransaction', () => {
                         accounts: null,
                         err: null,
                         innerInstructions: null,
+                        loadedAccountsDataSize: expect.any(Number),
                         logs: expect.any(Array),
                         replacementBlockhash: null,
                         returnData: null,
@@ -284,6 +285,7 @@ describe('simulateTransaction', () => {
                 accounts: null,
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -324,6 +326,7 @@ describe('simulateTransaction', () => {
                 accounts: null,
                 err: 'BlockhashNotFound',
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -364,6 +367,7 @@ describe('simulateTransaction', () => {
                 accounts: null,
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: {
                     blockhash: expect.any(String),
@@ -470,6 +474,7 @@ describe('simulateTransaction', () => {
                 accounts: null,
                 err: 'AccountNotFound',
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -520,6 +525,7 @@ describe('simulateTransaction', () => {
                 ],
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -570,6 +576,7 @@ describe('simulateTransaction', () => {
                 ],
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -637,6 +644,7 @@ describe('simulateTransaction', () => {
                 ],
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -688,6 +696,7 @@ describe('simulateTransaction', () => {
                 ],
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -737,7 +746,7 @@ describe('simulateTransaction', () => {
                 ],
                 err: null,
                 innerInstructions: null,
-
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -793,6 +802,7 @@ describe('simulateTransaction', () => {
                 ],
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
@@ -834,6 +844,7 @@ describe('simulateTransaction', () => {
                 accounts: null,
                 err: null,
                 innerInstructions: null,
+                loadedAccountsDataSize: expect.any(Number),
                 logs: expect.any(Array),
                 replacementBlockhash: null,
                 returnData: null,
diff --git a/packages/rpc-api/src/index.ts b/packages/rpc-api/src/index.ts
index 815e3bf47..03690674f 100644
--- a/packages/rpc-api/src/index.ts
+++ b/packages/rpc-api/src/index.ts
@@ -343,6 +343,7 @@ function getAllowedNumericKeypaths(): AllowedNumericKeypaths<RpcApi<SolanaRpcApi
                 ['delinquent', KEYPATH_WILDCARD, 'commission'],
             ],
             simulateTransaction: [
+                ['value', 'loadedAccountsDataSize'],
                 ...jsonParsedAccountsConfigs.map(c => ['value', 'accounts', KEYPATH_WILDCARD, ...c]),
                 ...innerInstructionsConfigs.map(c => ['value', 'innerInstructions', KEYPATH_WILDCARD, ...c]),
             ],
diff --git a/packages/rpc-api/src/simulateTransaction.ts b/packages/rpc-api/src/simulateTransaction.ts
index 0d88f2fd8..f3aec66aa 100644
--- a/packages/rpc-api/src/simulateTransaction.ts
+++ b/packages/rpc-api/src/simulateTransaction.ts
@@ -94,6 +94,8 @@ type WithInnerInstructionsConfig = Readonly<{
 type SimulateTransactionApiResponseBase = Readonly<{
     /** If the transaction failed, this property will contain the error */
     err: TransactionError | null;
+    /** The number of bytes of all accounts loaded by this transaction */
+    loadedAccountsDataSize?: number;
     /**
      * Array of log messages the transaction instructions output during execution, `null` if
      * simulation failed before the transaction was able to execute (for example due to an invalid