BTC crypto exchanges and BTC web wallets market volume. InChain potential market.

The potential market volume includes all BTC stored in the web wallets and crypto exchanges by the active users. I will take into account all the web wallets and all the crypto exchanges.
Several sources of information are available.

First. p2sh.info

The site shows statistics for 'pay to script hash' accounts. Usually major exchanges and some wallets store their BTC assets at the above type accounts to maintain the maximum security possible. Not all the p2sh accounts belong to exchanges and web wallets of course. At the same time the exchanges store their assets at p2sh accounts partially (only a part of their bitcoins are stored in p2sh accounts). I can also assume not all the exchanges use p2sh accounts.
In 2016 the biggest bitcoin volume held in p2sh accounts was about 2M BTC that is appr. 12% of all bitcoins.

So the total potential market volume should be around 2M BTC or more.

Second. Bitfinex hack
Bitfinex reports the loss of 120K btc and announced 36% haircut (http://www.coindesk.com/bitfinex-most-user-funds-offline/). So they lost more than 36% of the users deposits. They had their own 'security fund' that was used to cover some losses. Let's assume 120K is 50% of the Bitfinex BTC deposits. 240K BTC was held by Bitfinex before the hack. It's evident their deposits volume is lower now, let's say it is
(240K - 240K*0.36) - (some amount withdrawn after the hack by unhappy users) = 110K BTC (my estimation). If we know Bitfinex market share comparing to another exchanges we can estimate the total market volume.
One of the sources that can help is https://www.coinhills.com/market/exchange/
Both Chinese and non-Chinese exchanges are presented at the chart. Let's assume we can't directly compare Chinese and non-Chinese exchanges by the daily trading volume because they have absolutely different user trading scenarios. If we just take the daily trading volumes and assume they directly correspond to their total deposits the numbers won't be true. For example if Bitfinex total deposits share is 0.18% the total deposits amount of all the exchanges woul be 110K/0.0018 = 61M BTC which is of course incorrect. So I will exclude the major Chinese exchanges from the comparison. My calculations based on 24h trading volume resulted in 7% Bitfinex total market share and the total non-Chinese exchanges market is 1.58M BTC.
The real exchanges market is bigger but the number we have is good for the lower market limit estimation.

Third. BitcoinRichList

The major exchanges main storage accounts should have a balance of more than 1000 BTC. It's inconvenient to operate with smaller amounts. For example, 110K BTC of Bitfinex funds would require 110 different wallets of 1000 BTC each. I think it's easier to create 1-10 multisignature wallets than 110 smaller ones. There are also accounts that hold funds for daily in-out operations, I will just ignore them. This is acceptable because I can't distinguish exchanges accounts and all other accounts just by their amount, so some 'unwanted' accounts can be included in my estimation too.

To get the upper limit of the total exchanges market I will take the accounts from 1 000 to 100 000 BTC. In sum they hold 6.57M BTC. I don't know who holds those 122 accounts worth of 3M BTC but I include them anyway. We need to estimate how many bitcoins from 6.57M are held by the exchanges. I would say the truth is somewhere between 1.58M and 6.57M. I will take the average and get approximately 4M BTC.

This number is very close to the daily BTC trading volume according to https://www.coinhills.com. It makes me think I'm on the right way.

So my conclusion is that the total BTC amount stored at the exchanges is less than 4M BTC. I mean ALL the exchanges that exist on the market.

We should not also forget about the web wallets. I think the majority of users don't hold more than 10 btc at their web wallets. Let's assume the web wallets market share is 50% so the total volume of BTC stored at web wallets will be 1.3M*0.5 = 0.65M BTC.

Final result: 4.65M BTC

InChain market estimation.
We can roughly estimate the share of 12 exchanges/wallets offered by InChain.
Exchanges: Coinbase, Poloniex, Kraken, Yobit, Bittrex, BTC-e. I will use Bitfinex 110K balance assumption and the exhanges market shares from https://www.coinhills.com.
The exact numbers change on a daily basis but we just need a rough estimation. My calculations show 861K BTC.
Wallets: Blockchain.info, jaxx, mycelium, electrum, coinomi. Let's assume their total share is 20%. So their bitcoin market is 0.65*0.2 = 130K BTC.

The sum of the above two markets is 861+130 = 991K BTC that is almost 1M BTC.

The whole amount of funds that can be potentially insured by InChain is 1M BTC.