This function will return the available memory in bytes:
#import <mach/mach.h>
#import <mach/mach_host.h>
natural_t freeMemory(void) {
mach_port_t host_port = mach_host_self();
mach_msg_type_number_t host_size = sizeof(vm_statistics_data_t) / sizeof(integer_t);
vm_size_t pagesize;
vm_statistics_data_t vm_stat;
host_page_size(host_port, &pagesize);
if (host_statistics(host_port, HOST_VM_INFO, (host_info_t)&vm_stat, &host_size) != KERN_SUCCESS) NSLog(@"Failed to fetch vm statistics");
natural_t mem_used = (vm_stat.active_count + vm_stat.inactive_count + vm_stat.wire_count) * pagesize;
natural_t mem_free = vm_stat.free_count * pagesize;
natural_t mem_total = mem_used + mem_free;
return mem_free;
}