diff --git a/include/sys/debug.h b/include/sys/debug.h
index 9fabc4e..8c9d1c6 100644
--- a/include/sys/debug.h
+++ b/include/sys/debug.h
@@ -23,6 +23,8 @@
 #define kfatal(f, ...) debugf(DEBUG_FATAL, "[%s] " f, __func__, ##__VA_ARGS__)
 #define kprint(l, f, ...) debugf(l, "[%s] " f, __func__, ##__VA_ARGS__)
 
+void fmtsiz(char *buf, size_t sz);
+
 void debugc(int level, char c);
 void debugs(int level, const char *s);
 
diff --git a/sys/amd64/mm/heap.c b/sys/amd64/mm/heap.c
index 9ca4c30..4214180 100644
--- a/sys/amd64/mm/heap.c
+++ b/sys/amd64/mm/heap.c
@@ -118,6 +118,6 @@ void amd64_heap_dump(const heap_t *heap) {
          block; block = block->next) {
         assert((block->magic & HEAP_MAGIC) == HEAP_MAGIC, "Corrupted heap block magic\n");
 
-        kdebug("%p: %u %s%s\n", block, block->size, (block->magic & 1 ? "USED" : "FREE"), (block->next ? " -> " : ""));
+        kdebug("%p: %S %s%s\n", block, block->size, (block->magic & 1 ? "USED" : "FREE"), (block->next ? " -> " : ""));
     }
 }
diff --git a/sys/amd64/mm/mm.c b/sys/amd64/mm/mm.c
index d6c9d9f..0b5ba76 100644
--- a/sys/amd64/mm/mm.c
+++ b/sys/amd64/mm/mm.c
@@ -41,9 +41,9 @@ void amd64_mm_init(void) {
 
     // Allocate some pages for kernel heap (base size: 16MiB)
     uintptr_t heap_base_phys = amd64_phys_alloc_contiguous(KERNEL_HEAP >> 12);
-    // TODO: pretty-print sizes
-    assert(heap_base_phys != MM_NADDR, "Could not allocate %uKiB of memory for kernel heap\n", KERNEL_HEAP >> 10);
-    kdebug("Setting up kernel heap of %uKiB @ %p\n", KERNEL_HEAP >> 10, heap_base_phys);
+    assert(heap_base_phys != MM_NADDR, "Could not allocate %S of memory for kernel heap\n", KERNEL_HEAP);
+    kdebug("Setting up kernel heap of %S @ %p\n", KERNEL_HEAP, heap_base_phys);
     amd64_heap_init(heap_global, heap_base_phys, KERNEL_HEAP);
+
     amd64_heap_dump(heap_global);
 }
diff --git a/sys/amd64/mm/phys.c b/sys/amd64/mm/phys.c
index 7c649c3..5ab94b8 100644
--- a/sys/amd64/mm/phys.c
+++ b/sys/amd64/mm/phys.c
@@ -65,7 +65,7 @@ void amd64_phys_free(uintptr_t page) {
 // XXX: very slow impl.
 uintptr_t amd64_phys_alloc_contiguous(size_t count) {
     uintptr_t addr = 0;
-    kdebug("Requested %luKiB\n", count << 2);
+    kdebug("Requested %S\n", count << 12);
 
     if (count >= (PHYS_MAX_INDEX << 6)) {
         // The requested range is too large
@@ -115,8 +115,7 @@ void amd64_phys_memory_map(const multiboot_memory_map_t *mmap, size_t length) {
         uintptr_t page_aligned_end = (entry->addr + entry->len) & ~0xFFF;
 
         if (entry->type == 1 && page_aligned_end > page_aligned_begin) {
-            // TODO: size pretty-printing
-            kdebug("+++ %uKiB @ %p\n", (page_aligned_end - page_aligned_begin) / 1024, page_aligned_begin);
+            kdebug("+++ %S @ %p\n", page_aligned_end - page_aligned_begin, page_aligned_begin);
 
             for (uintptr_t addr = page_aligned_begin - PHYS_ALLOWED_BEGIN;
                  addr < (page_aligned_end - PHYS_ALLOWED_BEGIN); addr += 0x1000) {
@@ -133,6 +132,5 @@ void amd64_phys_memory_map(const multiboot_memory_map_t *mmap, size_t length) {
         curr_item += entry->size + sizeof(uint32_t);
     }
 
-    // TODO: size pretty-printing
-    kdebug("%uKiB available\n", total_phys << 2);
+    kdebug("%S available\n", total_phys << 12);
 }
diff --git a/sys/debug.c b/sys/debug.c
index dfe2c9d..e6aa58f 100644
--- a/sys/debug.c
+++ b/sys/debug.c
@@ -10,6 +10,34 @@
 static const char *s_debug_xs_set0 = "0123456789abcdef";
 static const char *s_debug_xs_set1 = "0123456789ABCDEF";
 
+void fmtsiz(char *out, size_t sz) {
+    static const char sizs[] = "KMGTPE???";
+    size_t f = sz, r = 0;
+    int pwr = 0;
+    size_t l = 0;
+
+    while (f >= 1536) {
+        r = ((f % 1024) * 10) / 1024;
+        f /= 1024;
+        ++pwr;
+    }
+
+    debug_ds(f, out, 0, 0);
+    l = strlen(out);
+
+    if (pwr) {
+        out[l++] = '.';
+        out[l++] = '0' + r;
+
+        out[l++] = sizs[pwr - 1];
+
+        out[l++] = 'i';
+    }
+
+    out[l++] = 'B';
+    out[l++] = 0;
+}
+
 // TODO: make debugc a __weak function of a character
 void debugc(int level, char c) {
 #if defined(ARCH_AMD64)
@@ -233,6 +261,11 @@ void debugfv(int level, const char *fmt, va_list args) {
                         debug_xs(value.v_ptr, buf, s_debug_xs_set0);
                         debugspl(level, buf, '0', sizeof(uintptr_t) * 2);
                         break;
+                    case 'S':
+                        value.v_ptr = va_arg(args, uintptr_t);
+                        fmtsiz(buf, value.v_ptr);
+                        debugsp(level, buf, padc, padn);
+                        break;
                     case 's':
                         value.v_string = va_arg(args, const char *);
                         debugsp(level, value.v_string ? value.v_string : "(null)", padc, padn);