Mount Point Capacity Calculator
Calculate available capacity across multiple mount points sharing an underlying volume.
Inputs
Allocation Summary
20 GB (4%) remains unallocated across mount points.
/boot
5.00GB
/ (root)
100.00GB
/home
200.00GB
/var
150.00GB
/tmp
25.00GB
Unallocated
20.00GB
Step by step
Values used
Total Disk Capacity (GB) = 500; /boot Allocation (%) = 1; / (root) Allocation (%) = 20; /home Allocation (%) = 40; /var Allocation (%) = 30; /tmp Allocation (%) = 5
Per-mount capacity
mount_capacity = total_capacity × allocation_percent
Allocation Summary
= 20 GB (4%) remains unallocated across mount points.
/boot
= 5.00 GB
/ (root)
= 100.00 GB
/home
= 200.00 GB
/var
= 150.00 GB
/tmp
= 25.00 GB
How it works
When a single disk is carved into separate mount points (either as distinct partitions or LVM logical volumes), each mount point's capacity is a fixed share of the underlying device — unlike directories on a shared filesystem, exceeding one mount point's allocation doesn't borrow from another. This calculator distributes total disk capacity across the standard Linux mount points (/boot, /, /home, /var, /tmp) by percentage share so you can plan partition sizes before running fdisk, parted or lvcreate.
Formula
Per-mount capacity
mount_capacity = total_capacity × allocation_percent
- T
- total disk capacity
- p_i
- allocation percentage for mount point i
Frequently Asked Questions
Why give /var its own partition?
/var holds logs, package caches and spool files that can grow unexpectedly (e.g. a runaway log). Isolating it on its own partition means a full /var can't consume all free space on / and crash the root filesystem or prevent login.
How big should /boot be?
/boot typically only needs 500MB-1GB even on modern systems, since it holds kernel images, initramfs and bootloader files. Percentage-based sizing works for planning, but /boot is usually better set to a fixed size regardless of total disk capacity.
Should swap be included as a mount point here?
No — swap space is a distinct partition type (or swap file) that isn't mounted into the directory tree, so it's sized separately. Use the Swap Size Calculator or Swap Partition Calculator for that allocation.