btrfs-calc-size: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/sbin/btrfs-calc-size - from package: btrfs-tools

You may install the required package with command apt-get install {package}

Error in other languages:
btrfs-calc-size: bevel nie gevind nie
btrfs-calc-size: comandă negăsită
btrfs-calc-size: comando não encontrado
btrfs-calc-size: commande introuvable
btrfs-calc-size: command not found
btrfs-calc-size: käsku ei ole
btrfs-calc-size: không tìm thấy lệnh
btrfs-calc-size: komanda nerasta
btrfs-calc-size: Kommando nicht gefunden.
btrfs-calc-size: kommandot finns inte
btrfs-calc-size: komut yok
btrfs-calc-size: nie znaleziono polecenia
btrfs-calc-size: níor aimsíodh an t-ordú
btrfs-calc-size: no se encontró la orden
btrfs-calc-size: no s'ha trobat l'ordre
btrfs-calc-size: opdracht niet gevonden
btrfs-calc-size: parancs nem található
btrfs-calc-size: perintah tidak ditemukan
btrfs-calc-size: príkaz nenájdený
btrfs-calc-size: příkaz nenalezen
btrfs-calc-size: команда не найдена
btrfs-calc-size: командата не е открита
btrfs-calc-size: 命令找不到
btrfs-calc-size: コマンドが見つかりません