How to know the size of a json object?

Question

This is my schema for my scoreboard application on mongodb. Now I cannot understand one thing that how would I make sure that this will not go higher than 16mb in size in mongodb the conditions are:

1. you can only make 10 teams in championship
2. one team can only have 12 players.
3. points table will be very small as the no of teams
4. matches and history array will have a lot of data

so this is the problem

championships{
    "ChampionShip_Name":"IPL",
    "overs":"10",
    "config":[true,true,true],
    "NoofTeams":12,
    "teams":[{
            "teamname":"chennai superkings",
            "players":[{
                "playername":"sachin tendulkar",
                "skills":["batting","bowling"],
                "position":"opener"
            }]
            },{
            "teamname":"rajasthan royals",
            "players":[{
                "playername":"virendra sehwag",
                "skills":["batting","bowling"],
                "position":"opener"
            }]
            }],
    "pointstable":[

    ],
    "matchlist":[{
    "team1":"chennai superkings",
    "team2":"rajasthan royals",
    "winner":"rajasthan royals",
    "winningtag":"rajsthan royals won by 10"
    "inining1":["123","45.5","5"],
    "inining2":["124","12","4"]
    }]
}
Scoreboard{
team1:"indian",
team2:"pakistan",
inings:[{
batting:{
},
bowling:{
}
},{
batting:{
},
bowling:{
}
}
]
}