diff --git a/crates/blockifier/src/execution/entry_point.rs b/crates/blockifier/src/execution/entry_point.rs
index f22f97ff3b..6fa7dea549 100644
--- a/crates/blockifier/src/execution/entry_point.rs
+++ b/crates/blockifier/src/execution/entry_point.rs
@@ -26,7 +26,7 @@ use crate::execution::execution_utils::execute_entry_point_call_wrapper;
 use crate::state::state_api::State;
 use crate::transaction::objects::{HasRelatedFeeType, TransactionInfo};
 use crate::transaction::transaction_types::TransactionType;
-use crate::utils::usize_from_u128;
+use crate::utils::usize_from_u64;
 use crate::versioned_constants::{GasCosts, VersionedConstants};
 
 #[cfg(test)]
@@ -209,14 +209,19 @@ impl EntryPointExecutionContext {
         // Use saturating upper bound to avoid overflow. This is safe because the upper bound is
         // bounded above by the block's limit, which is a usize.
 
-        let upper_bound_u128 = if gas_per_step.is_zero() {
-            u128::MAX
+        let upper_bound_u64 = if gas_per_step.is_zero() {
+            u64::MAX
         } else {
-            (gas_per_step.inv() * tx_gas_upper_bound.0).to_integer()
+            // TODO: This panic will disappear once GasAmount is a u64.
+            (gas_per_step.inv()
+                * u64::try_from(tx_gas_upper_bound.0).unwrap_or_else(|_| {
+                    panic!("Gas amounts cannot be more than 64 bits; got {tx_gas_upper_bound:?}.")
+                }))
+            .to_integer()
         };
-        let tx_upper_bound = usize_from_u128(upper_bound_u128).unwrap_or_else(|_| {
+        let tx_upper_bound = usize_from_u64(upper_bound_u64).unwrap_or_else(|_| {
             log::warn!(
-                "Failed to convert u128 to usize: {upper_bound_u128}. Upper bound from tx is \
+                "Failed to convert u128 to usize: {upper_bound_u64}. Upper bound from tx is \
                  {tx_gas_upper_bound:?}, gas per step is {gas_per_step}."
             );
             usize::MAX
diff --git a/crates/blockifier/src/fee/fee_test.rs b/crates/blockifier/src/fee/fee_test.rs
index a4ee436a77..296c5a711f 100644
--- a/crates/blockifier/src/fee/fee_test.rs
+++ b/crates/blockifier/src/fee/fee_test.rs
@@ -29,7 +29,7 @@ use crate::test_utils::{
     MAX_L1_GAS_AMOUNT,
 };
 use crate::transaction::test_utils::{account_invoke_tx, all_resource_bounds, l1_resource_bounds};
-use crate::utils::u128_from_usize;
+use crate::utils::{u128_from_usize, u64_from_usize};
 use crate::versioned_constants::VersionedConstants;
 
 fn get_vm_resource_usage() -> ExecutionResources {
@@ -57,12 +57,12 @@ fn test_simple_get_vm_resource_usage(
 
     // Positive flow.
     // Verify calculation - in our case, n_steps is the heaviest resource.
-    let vm_usage_in_l1_gas = GasAmount(
+    let vm_usage_in_l1_gas = GasAmount(u128::from(
         (versioned_constants.vm_resource_fee_cost().n_steps
-            * (u128_from_usize(vm_resource_usage.n_steps + n_reverted_steps)))
+            * (u64_from_usize(vm_resource_usage.n_steps + n_reverted_steps)))
         .ceil()
         .to_integer(),
-    );
+    ));
     let expected_gas_vector = gas_vector_from_vm_usage(
         vm_usage_in_l1_gas,
         &gas_vector_computation_mode,
@@ -113,12 +113,12 @@ fn test_float_get_vm_resource_usage(
     // Positive flow.
     // Verify calculation - in our case, n_steps is the heaviest resource.
     let n_reverted_steps = 300;
-    let vm_usage_in_l1_gas = GasAmount(
+    let vm_usage_in_l1_gas = GasAmount(u128::from(
         (versioned_constants.vm_resource_fee_cost().n_steps
-            * u128_from_usize(vm_resource_usage.n_steps + n_reverted_steps))
+            * u64_from_usize(vm_resource_usage.n_steps + n_reverted_steps))
         .ceil()
         .to_integer(),
-    );
+    ));
     let expected_gas_vector = gas_vector_from_vm_usage(
         vm_usage_in_l1_gas,
         &gas_vector_computation_mode,
@@ -136,14 +136,14 @@ fn test_float_get_vm_resource_usage(
 
     // Another positive flow, this time the heaviest resource is ecdsa_builtin.
     vm_resource_usage.n_steps = 200;
-    let vm_usage_in_l1_gas = GasAmount(
+    let vm_usage_in_l1_gas = GasAmount(u128::from(
         ((*versioned_constants.vm_resource_fee_cost().builtins.get(&BuiltinName::ecdsa).unwrap())
-            * u128_from_usize(
+            * u64_from_usize(
                 *vm_resource_usage.builtin_instance_counter.get(&BuiltinName::ecdsa).unwrap(),
             ))
         .ceil()
         .to_integer(),
-    );
+    ));
     let expected_gas_vector = gas_vector_from_vm_usage(
         vm_usage_in_l1_gas,
         &gas_vector_computation_mode,
diff --git a/crates/blockifier/src/fee/fee_utils.rs b/crates/blockifier/src/fee/fee_utils.rs
index c0081dd2f8..7251e90c00 100644
--- a/crates/blockifier/src/fee/fee_utils.rs
+++ b/crates/blockifier/src/fee/fee_utils.rs
@@ -18,7 +18,7 @@ use crate::fee::resources::{GasVector, TransactionFeeResult};
 use crate::state::state_api::StateReader;
 use crate::transaction::errors::TransactionFeeError;
 use crate::transaction::objects::{ExecutionResourcesTraits, FeeType, TransactionInfo};
-use crate::utils::u128_from_usize;
+use crate::utils::u64_from_usize;
 use crate::versioned_constants::VersionedConstants;
 
 #[cfg(test)]
@@ -51,7 +51,7 @@ pub fn get_vm_resources_cost(
 
     // Convert Cairo resource usage to L1 gas usage.
     // Do so by taking the maximum of the usage of each builtin + step usage.
-    let vm_l1_gas_usage = GasAmount(
+    let vm_l1_gas_usage = GasAmount(u128::from(
         vm_resource_fee_costs
         .builtins
         .iter()
@@ -64,9 +64,9 @@ pub fn get_vm_resources_cost(
             vm_resource_fee_costs.n_steps,
             vm_resource_usage.total_n_steps() + n_reverted_steps,
         )])
-        .map(|(cost, usage)| (cost * u128_from_usize(usage)).ceil().to_integer())
-        .fold(0, u128::max),
-    );
+        .map(|(cost, usage)| (cost * u64_from_usize(usage)).ceil().to_integer())
+        .fold(0, u64::max),
+    ));
 
     match computation_mode {
         GasVectorComputationMode::NoL2Gas => GasVector::from_l1_gas(vm_l1_gas_usage),
diff --git a/crates/blockifier/src/fee/gas_usage_test.rs b/crates/blockifier/src/fee/gas_usage_test.rs
index 013bc27d92..395e685518 100644
--- a/crates/blockifier/src/fee/gas_usage_test.rs
+++ b/crates/blockifier/src/fee/gas_usage_test.rs
@@ -16,7 +16,7 @@ use crate::state::cached_state::StateChangesCount;
 use crate::test_utils::{DEFAULT_ETH_L1_DATA_GAS_PRICE, DEFAULT_ETH_L1_GAS_PRICE};
 use crate::transaction::objects::FeeType;
 use crate::transaction::test_utils::account_invoke_tx;
-use crate::utils::u128_from_usize;
+use crate::utils::{u128_from_usize, u64_from_usize};
 use crate::versioned_constants::{ResourceCost, VersionedConstants};
 #[fixture]
 fn versioned_constants() -> &'static VersionedConstants {
@@ -90,7 +90,7 @@ fn test_get_event_gas_cost(
     let execution_summary = CallInfo::summarize_many(call_infos.iter());
     // 8 keys and 11 data words overall.
     let expected_gas =
-        GasAmount((data_word_cost * (event_key_factor * 8_u128 + 11_u128)).to_integer());
+        GasAmount(u128::from((data_word_cost * (event_key_factor * 8_u64 + 11_u64)).to_integer()));
     let expected_gas_vector = match gas_vector_computation_mode {
         GasVectorComputationMode::NoL2Gas => GasVector::from_l1_gas(expected_gas),
         GasVectorComputationMode::All => GasVector::from_l2_gas(expected_gas),
@@ -195,7 +195,10 @@ fn test_onchain_data_discount() {
 
     let cost_without_discount = (state_changes_count.n_storage_updates * 2) * (512 + 100);
     let actual_cost = get_da_gas_cost(&state_changes_count, use_kzg_da).l1_gas;
-    let cost_ratio = ResourceCost::new(actual_cost.0, u128_from_usize(cost_without_discount));
+    let cost_ratio = ResourceCost::new(
+        u64::try_from(actual_cost.0).unwrap(),
+        u64_from_usize(cost_without_discount),
+    );
     assert!(cost_ratio <= ResourceCost::new(9, 10));
     assert!(cost_ratio >= ResourceCost::new(88, 100));
 }
diff --git a/crates/blockifier/src/fee/receipt_test.rs b/crates/blockifier/src/fee/receipt_test.rs
index 4cbe47a677..bf5d5f8c90 100644
--- a/crates/blockifier/src/fee/receipt_test.rs
+++ b/crates/blockifier/src/fee/receipt_test.rs
@@ -31,7 +31,7 @@ use crate::transaction::test_utils::{
     create_resource_bounds,
 };
 use crate::transaction::transactions::ExecutableTransaction;
-use crate::utils::{u128_from_usize, usize_from_u128};
+use crate::utils::{u128_from_usize, u64_from_usize, usize_from_u128};
 use crate::versioned_constants::VersionedConstants;
 
 #[fixture]
@@ -82,15 +82,15 @@ fn test_calculate_tx_gas_usage_basic<'a>(
         let gas_per_code_byte = versioned_constants
             .get_archival_data_gas_costs(&gas_vector_computation_mode)
             .gas_per_code_byte;
-        let code_gas_cost = GasAmount(
+        let code_gas_cost = GasAmount(u128::from(
             (gas_per_code_byte
-                * u128_from_usize(
+                * u64_from_usize(
                     (class_info.bytecode_length() + class_info.sierra_program_length())
                         * eth_gas_constants::WORD_WIDTH
                         + class_info.abi_length(),
                 ))
             .to_integer(),
-        );
+        ));
         let manual_gas_vector = match gas_vector_computation_mode {
             GasVectorComputationMode::NoL2Gas => GasVector::from_l1_gas(code_gas_cost),
             GasVectorComputationMode::All => GasVector::from_l2_gas(code_gas_cost),
@@ -126,9 +126,9 @@ fn test_calculate_tx_gas_usage_basic<'a>(
     let gas_per_data_felt = versioned_constants
         .get_archival_data_gas_costs(&gas_vector_computation_mode)
         .gas_per_data_felt;
-    let calldata_and_signature_gas_cost = (gas_per_data_felt
-        * u128_from_usize(calldata_length + signature_length))
-    .to_integer()
+    let calldata_and_signature_gas_cost = u128::from(
+        (gas_per_data_felt * u64_from_usize(calldata_length + signature_length)).to_integer(),
+    )
     .into();
     let manual_starknet_gas_usage_vector = match gas_vector_computation_mode {
         GasVectorComputationMode::NoL2Gas => {
@@ -165,9 +165,10 @@ fn test_calculate_tx_gas_usage_basic<'a>(
 
     // Manual calculation.
     let message_segment_length = get_message_segment_length(&[], Some(l1_handler_payload_size));
-    let calldata_and_signature_gas_cost = (gas_per_data_felt
-        * u128_from_usize(l1_handler_payload_size + signature_length))
-    .to_integer()
+    let calldata_and_signature_gas_cost = u128::from(
+        (gas_per_data_felt * u64_from_usize(l1_handler_payload_size + signature_length))
+            .to_integer(),
+    )
     .into();
     let calldata_and_signature_gas_cost_vector = match gas_vector_computation_mode {
         GasVectorComputationMode::NoL2Gas => {
diff --git a/crates/blockifier/src/fee/resources.rs b/crates/blockifier/src/fee/resources.rs
index fa0d105f70..401e2f3da1 100644
--- a/crates/blockifier/src/fee/resources.rs
+++ b/crates/blockifier/src/fee/resources.rs
@@ -19,8 +19,12 @@ use crate::fee::gas_usage::{
 use crate::state::cached_state::{StateChanges, StateChangesCount};
 use crate::transaction::errors::TransactionFeeError;
 use crate::transaction::objects::HasRelatedFeeType;
-use crate::utils::u128_from_usize;
-use crate::versioned_constants::{ArchivalDataGasCosts, VersionedConstants};
+use crate::utils::{u128_from_usize, u64_from_usize};
+use crate::versioned_constants::{
+    resource_cost_to_u128_ratio,
+    ArchivalDataGasCosts,
+    VersionedConstants,
+};
 
 pub type TransactionFeeResult<T> = Result<T, TransactionFeeError>;
 
@@ -203,21 +207,25 @@ impl ArchivalDataResources {
         archival_gas_costs: &ArchivalDataGasCosts,
     ) -> GasAmount {
         // TODO(Avi, 20/2/2024): Calculate the number of bytes instead of the number of felts.
-        let total_data_size = u128_from_usize(self.calldata_length + self.signature_length);
-        GasAmount((archival_gas_costs.gas_per_data_felt * total_data_size).to_integer())
+        let total_data_size = u64_from_usize(self.calldata_length + self.signature_length);
+        GasAmount(u128::from((archival_gas_costs.gas_per_data_felt * total_data_size).to_integer()))
     }
 
     /// Returns the cost of declared class codes in L1/L2 gas units, depending on the mode.
     fn get_code_gas_cost(&self, archival_gas_costs: &ArchivalDataGasCosts) -> GasAmount {
-        (archival_gas_costs.gas_per_code_byte * u128_from_usize(self.code_size)).to_integer().into()
+        u128::from(
+            (archival_gas_costs.gas_per_code_byte * u64_from_usize(self.code_size)).to_integer(),
+        )
+        .into()
     }
 
     /// Returns the cost of the transaction's emmited events in L1/L2 gas units, depending on the
     /// mode.
     fn get_events_gas_cost(&self, archival_gas_costs: &ArchivalDataGasCosts) -> GasAmount {
         GasAmount(
-            (archival_gas_costs.gas_per_data_felt
-                * (archival_gas_costs.event_key_factor * self.event_summary.total_event_keys
+            (resource_cost_to_u128_ratio(archival_gas_costs.gas_per_data_felt)
+                * (resource_cost_to_u128_ratio(archival_gas_costs.event_key_factor)
+                    * self.event_summary.total_event_keys
                     + self.event_summary.total_event_data_size))
                 .to_integer(),
         )
diff --git a/crates/blockifier/src/test_utils.rs b/crates/blockifier/src/test_utils.rs
index c96562f848..af8e837997 100644
--- a/crates/blockifier/src/test_utils.rs
+++ b/crates/blockifier/src/test_utils.rs
@@ -382,10 +382,6 @@ pub fn create_trivial_calldata(test_contract_address: ContractAddress) -> Callda
     )
 }
 
-pub fn u64_from_usize(val: usize) -> u64 {
-    val.try_into().unwrap()
-}
-
 pub fn update_json_value(base: &mut serde_json::Value, update: serde_json::Value) {
     match (base, update) {
         (serde_json::Value::Object(base_map), serde_json::Value::Object(update_map)) => {
diff --git a/crates/blockifier/src/transaction/errors.rs b/crates/blockifier/src/transaction/errors.rs
index 7f8887477c..911b4c64aa 100644
--- a/crates/blockifier/src/transaction/errors.rs
+++ b/crates/blockifier/src/transaction/errors.rs
@@ -166,4 +166,6 @@ pub enum ParseError {
 pub enum NumericConversionError {
     #[error("Conversion of {0} to u128 unsuccessful.")]
     U128ToUsizeError(u128),
+    #[error("Conversion of {0} to u64 unsuccessful.")]
+    U64ToUsizeError(u64),
 }
diff --git a/crates/blockifier/src/utils.rs b/crates/blockifier/src/utils.rs
index 5a75bc5e2d..9e70cf5f90 100644
--- a/crates/blockifier/src/utils.rs
+++ b/crates/blockifier/src/utils.rs
@@ -54,8 +54,20 @@ pub fn usize_from_u128(val: u128) -> Result<usize, NumericConversionError> {
     val.try_into().map_err(|_| NumericConversionError::U128ToUsizeError(val))
 }
 
+/// Conversion from u64 to usize. This conversion should only be used if the value came from a
+/// usize.
+pub fn usize_from_u64(val: u64) -> Result<usize, NumericConversionError> {
+    val.try_into().map_err(|_| NumericConversionError::U64ToUsizeError(val))
+}
+
 /// Conversion from usize to u128. May fail on architectures with over 128 bits
 /// of address space.
 pub fn u128_from_usize(val: usize) -> u128 {
     val.try_into().expect("Conversion from usize to u128 should not fail.")
 }
+
+/// Conversion from usize to u64. May fail on architectures with over 64 bits
+/// of address space.
+pub fn u64_from_usize(val: usize) -> u64 {
+    val.try_into().expect("Conversion from usize to u64 should not fail.")
+}
diff --git a/crates/blockifier/src/versioned_constants.rs b/crates/blockifier/src/versioned_constants.rs
index eecc5b7c25..0fa67976d4 100644
--- a/crates/blockifier/src/versioned_constants.rs
+++ b/crates/blockifier/src/versioned_constants.rs
@@ -135,7 +135,12 @@ define_versioned_constants! {
     V0_13_3
 }
 
-pub type ResourceCost = Ratio<u128>;
+pub type ResourceCost = Ratio<u64>;
+
+pub fn resource_cost_to_u128_ratio(cost: ResourceCost) -> Ratio<u128> {
+    Ratio::new((*cost.numer()).into(), (*cost.denom()).into())
+}
+
 #[derive(Clone, Debug, Deserialize, Eq, PartialEq, PartialOrd)]
 pub struct CompilerVersion(pub Version);
 impl Default for CompilerVersion {
@@ -222,18 +227,26 @@ impl VersionedConstants {
 
     /// Converts from L1 gas price to L2 gas price with **upward rounding**.
     pub fn convert_l1_to_l2_gas_price_round_up(&self, l1_gas_price: GasPrice) -> GasPrice {
-        GasPrice(*(self.l1_to_l2_gas_price_ratio() * l1_gas_price.0).ceil().numer())
+        GasPrice(
+            *(resource_cost_to_u128_ratio(self.l1_to_l2_gas_price_ratio()) * l1_gas_price.0)
+                .ceil()
+                .numer(),
+        )
     }
 
     /// Converts from L1 gas amount to L2 gas amount with **upward rounding**.
     pub fn convert_l1_to_l2_gas_amount_round_up(&self, l1_gas_amount: GasAmount) -> GasAmount {
         // The amount ratio is the inverse of the price ratio.
-        GasAmount(*(self.l1_to_l2_gas_price_ratio().inv() * l1_gas_amount.0).ceil().numer())
+        GasAmount(
+            *(resource_cost_to_u128_ratio(self.l1_to_l2_gas_price_ratio().inv()) * l1_gas_amount.0)
+                .ceil()
+                .numer(),
+        )
     }
 
     /// Returns the following ratio: L2_gas_price/L1_gas_price.
     fn l1_to_l2_gas_price_ratio(&self) -> ResourceCost {
-        Ratio::new(1, u128::from(self.os_constants.gas_costs.step_gas_cost))
+        Ratio::new(1, self.os_constants.gas_costs.step_gas_cost)
             * self.vm_resource_fee_cost().n_steps
     }