diff --git a/src/core/payments/constants.ts b/src/core/payments/constants.ts
index 6f044cc..924cb5b 100644
--- a/src/core/payments/constants.ts
+++ b/src/core/payments/constants.ts
@@ -51,3 +51,9 @@ export const BUFFER_DENOMINATOR = 10n
  */
 export const STORAGE_SCALE_MAX = 10_000_000
 export const STORAGE_SCALE_MAX_BI = BigInt(STORAGE_SCALE_MAX)
+
+/** PDP Leaf Size - the payment rate is based on `rawSize` bytes rounded up to the next multiple of 32.
+ *
+ * @see - https://github.com/FilOzone/synapse-sdk/issues/339#issue-3539254596
+ */
+export const PDP_LEAF_SIZE = 32
diff --git a/src/core/payments/index.ts b/src/core/payments/index.ts
index 2100abc..1e0354a 100644
--- a/src/core/payments/index.ts
+++ b/src/core/payments/index.ts
@@ -32,6 +32,7 @@ import {
 } from './constants.js'
 import { applyFloorPricing } from './floor-pricing.js'
 import type { PaymentStatus, ServiceApprovalStatus, StorageAllowances, StorageRunwaySummary } from './types.js'
+import { padSizeToPDPLeaves } from './utils.js'
 
 // Re-export all constants
 export * from './constants.js'
@@ -826,7 +827,8 @@ export function calculateDepositCapacity(
  * @returns Required allowances for the piece
  */
 export function calculateRequiredAllowances(pieceSizeBytes: number, pricePerTiBPerEpoch: bigint): StorageAllowances {
-  const storageTiB = pieceSizeBytes / Number(SIZE_CONSTANTS.TiB)
+  const paddedSizeBytes = padSizeToPDPLeaves(pieceSizeBytes)
+  const storageTiB = paddedSizeBytes / Number(SIZE_CONSTANTS.TiB)
   return calculateStorageAllowances(storageTiB, pricePerTiBPerEpoch)
 }
 
diff --git a/src/core/payments/utils.ts b/src/core/payments/utils.ts
new file mode 100644
index 0000000..500a930
--- /dev/null
+++ b/src/core/payments/utils.ts
@@ -0,0 +1,11 @@
+import { PDP_LEAF_SIZE } from './constants.js'
+
+/**
+ * Pad raw size to the next multiple of 32 bytes
+ *
+ * @param rawSizeBytes - The actual size in bytes
+ * @returns Padded size (next multiple of 32)
+ */
+export function padSizeToPDPLeaves(rawSizeBytes: number): number {
+  return Math.ceil(rawSizeBytes / PDP_LEAF_SIZE) * PDP_LEAF_SIZE
+}