diff --git a/README.md b/README.md
index d6faf411..e3fbffce 100644
--- a/README.md
+++ b/README.md
@@ -35,6 +35,7 @@ let mut allocator = Allocator::new(&AllocatorCreateDesc {
     physical_device,
     debug_settings: Default::default(),
     buffer_device_address: true,  // Ideally, check the BufferDeviceAddressFeatures struct.
+    allocation_sizes: Default::default(),
 });
 ```
 
@@ -78,6 +79,7 @@ use gpu_allocator::d3d12::*;
 let mut allocator = Allocator::new(&AllocatorCreateDesc {
     device,
     debug_settings: Default::default(),
+    allocation_sizes: Default::default(),
 });
 ```
 
diff --git a/examples/d3d12-buffer-winrs.rs b/examples/d3d12-buffer-winrs.rs
index 423b38ab..deb7d94d 100644
--- a/examples/d3d12-buffer-winrs.rs
+++ b/examples/d3d12-buffer-winrs.rs
@@ -90,6 +90,7 @@ fn main() -> Result<()> {
     let mut allocator = Allocator::new(&AllocatorCreateDesc {
         device: device.clone(),
         debug_settings: Default::default(),
+        allocation_sizes: Default::default(),
     })
     .unwrap();
 
diff --git a/examples/d3d12-buffer.rs b/examples/d3d12-buffer.rs
index 26bb9b67..bd9ff2df 100644
--- a/examples/d3d12-buffer.rs
+++ b/examples/d3d12-buffer.rs
@@ -119,6 +119,7 @@ fn main() {
     let mut allocator = Allocator::new(&AllocatorCreateDesc {
         device: device.as_windows().clone(),
         debug_settings: Default::default(),
+        allocation_sizes: Default::default(),
     })
     .unwrap();
 
diff --git a/examples/d3d12-visualization/main.rs b/examples/d3d12-visualization/main.rs
index e9bb1849..a364a786 100644
--- a/examples/d3d12-visualization/main.rs
+++ b/examples/d3d12-visualization/main.rs
@@ -358,6 +358,7 @@ fn main() {
         let mut allocator = Allocator::new(&AllocatorCreateDesc {
             device: device.as_windows().clone(),
             debug_settings: Default::default(),
+            allocation_sizes: Default::default(),
         })
         .unwrap();
 
diff --git a/examples/vulkan-buffer.rs b/examples/vulkan-buffer.rs
index 3a5e3762..b2175de9 100644
--- a/examples/vulkan-buffer.rs
+++ b/examples/vulkan-buffer.rs
@@ -98,6 +98,7 @@ fn main() {
         physical_device: pdevice,
         debug_settings: Default::default(),
         buffer_device_address: false,
+        allocation_sizes: Default::default(),
     })
     .unwrap();
 
diff --git a/examples/vulkan-visualization/main.rs b/examples/vulkan-visualization/main.rs
index de3cc42e..652a11d2 100644
--- a/examples/vulkan-visualization/main.rs
+++ b/examples/vulkan-visualization/main.rs
@@ -231,6 +231,7 @@ fn main() -> ash::prelude::VkResult<()> {
             physical_device: pdevice,
             debug_settings: Default::default(),
             buffer_device_address: false,
+            allocation_sizes: Default::default(),
         })
         .unwrap(),
     );
diff --git a/src/d3d12/mod.rs b/src/d3d12/mod.rs
index b02216ba..2a77b603 100644
--- a/src/d3d12/mod.rs
+++ b/src/d3d12/mod.rs
@@ -85,7 +85,8 @@ use super::allocator;
 use super::allocator::AllocationType;
 
 use crate::{
-    allocator::fmt_bytes, AllocationError, AllocatorDebugSettings, MemoryLocation, Result,
+    allocator::fmt_bytes, AllocationError, AllocationSizes, AllocatorDebugSettings, MemoryLocation,
+    Result,
 };
 
 /// [`ResourceCategory`] is used for supporting [`D3D12_RESOURCE_HEAP_TIER_1`].
@@ -231,6 +232,7 @@ impl<'a> AllocationCreateDesc<'a> {
 pub struct AllocatorCreateDesc {
     pub device: ID3D12Device,
     pub debug_settings: AllocatorDebugSettings,
+    pub allocation_sizes: AllocationSizes,
 }
 
 pub enum ResourceType<'a> {
@@ -386,21 +388,20 @@ struct MemoryType {
     active_general_blocks: usize,
 }
 
-const DEFAULT_DEVICE_MEMBLOCK_SIZE: u64 = 256 * 1024 * 1024;
-const DEFAULT_HOST_MEMBLOCK_SIZE: u64 = 64 * 1024 * 1024;
 impl MemoryType {
     fn allocate(
         &mut self,
         device: &ID3D12Device,
         desc: &AllocationCreateDesc<'_>,
         backtrace: Option<backtrace::Backtrace>,
+        allocation_sizes: &AllocationSizes,
     ) -> Result<Allocation> {
         let allocation_type = AllocationType::Linear;
 
         let memblock_size = if self.heap_properties.Type == D3D12_HEAP_TYPE_DEFAULT {
-            DEFAULT_DEVICE_MEMBLOCK_SIZE
+            allocation_sizes.device_memblock_size
         } else {
-            DEFAULT_HOST_MEMBLOCK_SIZE
+            allocation_sizes.host_memblock_size
         };
 
         let size = desc.size;
@@ -573,6 +574,7 @@ pub struct Allocator {
     device: ID3D12Device,
     debug_settings: AllocatorDebugSettings,
     memory_types: Vec<MemoryType>,
+    allocation_sizes: AllocationSizes,
 }
 
 impl Allocator {
@@ -679,6 +681,7 @@ impl Allocator {
             memory_types,
             device,
             debug_settings: desc.debug_settings,
+            allocation_sizes: desc.allocation_sizes,
         })
     }
 
@@ -722,7 +725,7 @@ impl Allocator {
             })
             .ok_or(AllocationError::NoCompatibleMemoryTypeFound)?;
 
-        memory_type.allocate(&self.device, desc, backtrace)
+        memory_type.allocate(&self.device, desc, backtrace, &self.allocation_sizes)
     }
 
     pub fn free(&mut self, allocation: Allocation) -> Result<()> {
diff --git a/src/lib.rs b/src/lib.rs
index 04096d20..f23acc94 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -24,6 +24,7 @@
 //!     physical_device,
 //!     debug_settings: Default::default(),
 //!     buffer_device_address: true,  // Ideally, check the BufferDeviceAddressFeatures struct.
+//!     allocation_sizes: Default::default(),
 //! });
 //! # }
 //! # #[cfg(not(feature = "vulkan"))]
@@ -48,6 +49,7 @@
 //! #     physical_device,
 //! #     debug_settings: Default::default(),
 //! #     buffer_device_address: true,  // Ideally, check the BufferDeviceAddressFeatures struct.
+//! #     allocation_sizes: Default::default(),
 //! # }).unwrap();
 //!
 //! // Setup vulkan info
@@ -89,6 +91,7 @@
 //! let mut allocator = Allocator::new(&AllocatorCreateDesc {
 //!     device,
 //!     debug_settings: Default::default(),
+//!     allocation_sizes: Default::default(),
 //! });
 //! # }
 //! # #[cfg(not(feature = "d3d12"))]
@@ -108,6 +111,7 @@
 //! # let mut allocator = Allocator::new(&AllocatorCreateDesc {
 //! #     device: device,
 //! #     debug_settings: Default::default(),
+//! #     allocation_sizes: Default::default(),
 //! # }).unwrap();
 //!
 //! let buffer_desc = Direct3D12::D3D12_RESOURCE_DESC {
@@ -210,3 +214,58 @@ impl Default for AllocatorDebugSettings {
         }
     }
 }
+
+/// The sizes of the memory blocks that the allocator will create.
+///
+/// Useful for tuning the allocator to your application's needs. For example most games will be fine with the default
+/// values, but eg. an app might want to use smaller block sizes to reduce the amount of memory used.
+///
+/// Clamped between 4MB and 256MB, and rounds up to the nearest multiple of 4MB for alignment reasons.
+#[derive(Clone, Copy, Debug)]
+pub struct AllocationSizes {
+    /// The size of the memory blocks that will be created for the GPU only memory type.
+    ///
+    /// Defaults to 256MB.
+    device_memblock_size: u64,
+    /// The size of the memory blocks that will be created for the CPU visible memory types.
+    ///
+    /// Defaults to 64MB.
+    host_memblock_size: u64,
+}
+
+impl AllocationSizes {
+    pub fn new(device_memblock_size: u64, host_memblock_size: u64) -> Self {
+        const FOUR_MB: u64 = 4 * 1024 * 1024;
+        const TWO_HUNDRED_AND_FIFTY_SIX_MB: u64 = 256 * 1024 * 1024;
+
+        let mut device_memblock_size =
+            device_memblock_size.clamp(FOUR_MB, TWO_HUNDRED_AND_FIFTY_SIX_MB);
+        let mut host_memblock_size = host_memblock_size.clamp(FOUR_MB, TWO_HUNDRED_AND_FIFTY_SIX_MB);
+
+        if device_memblock_size % FOUR_MB != 0 {
+            let val = device_memblock_size / FOUR_MB + 1;
+            device_memblock_size = val * FOUR_MB;
+            log::warn!("Device memory block size must be a multiple of 4MB, clamping to {}MB", device_memblock_size / 1024 / 1024)
+        }
+        
+        if host_memblock_size % FOUR_MB != 0 {
+            let val = host_memblock_size / FOUR_MB + 1;
+            host_memblock_size = val * FOUR_MB;
+            log::warn!("Host memory block size must be a multiple of 4MB, clamping to {}MB", host_memblock_size / 1024 / 1024)
+        }
+
+        Self {
+            device_memblock_size,
+            host_memblock_size,
+        }
+    }
+}
+
+impl Default for AllocationSizes {
+    fn default() -> Self {
+        Self {
+            device_memblock_size: 256 * 1024 * 1024,
+            host_memblock_size: 64 * 1024 * 1024,
+        }
+    }
+}
diff --git a/src/vulkan/mod.rs b/src/vulkan/mod.rs
index 2d0760a8..be90c930 100644
--- a/src/vulkan/mod.rs
+++ b/src/vulkan/mod.rs
@@ -13,7 +13,8 @@ use log::{debug, Level};
 use std::fmt;
 
 use crate::{
-    allocator::fmt_bytes, AllocationError, AllocatorDebugSettings, MemoryLocation, Result,
+    allocator::fmt_bytes, AllocationError, AllocationSizes, AllocatorDebugSettings, MemoryLocation,
+    Result,
 };
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq)]
@@ -61,6 +62,7 @@ pub struct AllocatorCreateDesc {
     pub physical_device: ash::vk::PhysicalDevice,
     pub debug_settings: AllocatorDebugSettings,
     pub buffer_device_address: bool,
+    pub allocation_sizes: AllocationSizes,
 }
 
 /// A piece of allocated memory.
@@ -441,9 +443,6 @@ pub(crate) struct MemoryType {
     pub(crate) buffer_device_address: bool,
 }
 
-const DEFAULT_DEVICE_MEMBLOCK_SIZE: u64 = 256 * 1024 * 1024;
-const DEFAULT_HOST_MEMBLOCK_SIZE: u64 = 64 * 1024 * 1024;
-
 impl MemoryType {
     fn allocate(
         &mut self,
@@ -451,6 +450,7 @@ impl MemoryType {
         desc: &AllocationCreateDesc<'_>,
         granularity: u64,
         backtrace: Option<backtrace::Backtrace>,
+        allocation_sizes: &AllocationSizes,
     ) -> Result<Allocation> {
         let allocation_type = if desc.linear {
             AllocationType::Linear
@@ -462,9 +462,9 @@ impl MemoryType {
             .memory_properties
             .contains(vk::MemoryPropertyFlags::HOST_VISIBLE)
         {
-            DEFAULT_HOST_MEMBLOCK_SIZE
+            allocation_sizes.host_memblock_size
         } else {
-            DEFAULT_DEVICE_MEMBLOCK_SIZE
+            allocation_sizes.device_memblock_size
         };
 
         let size = desc.requirements.size;
@@ -677,6 +677,7 @@ pub struct Allocator {
     device: ash::Device,
     pub(crate) buffer_image_granularity: u64,
     pub(crate) debug_settings: AllocatorDebugSettings,
+    allocation_sizes: AllocationSizes,
 }
 
 impl fmt::Debug for Allocator {
@@ -793,6 +794,7 @@ impl Allocator {
             device: desc.device.clone(),
             buffer_image_granularity: granularity,
             debug_settings: desc.debug_settings,
+            allocation_sizes: AllocationSizes::default(),
         })
     }
 
@@ -866,6 +868,7 @@ impl Allocator {
                 desc,
                 self.buffer_image_granularity,
                 backtrace.clone(),
+                &self.allocation_sizes,
             )
         };
 
@@ -887,6 +890,7 @@ impl Allocator {
                     desc,
                     self.buffer_image_granularity,
                     backtrace,
+                    &self.allocation_sizes,
                 )
             } else {
                 allocation