# How does Coinmarketcap calculate the USD price for Bitcoin?

I'm doing a school project in which I'm building my own bitcoin price index similar to coinmarketcap. I want to calculate the USD price for bitcoin by using volume weight averaging from multiple exchanges. Some of the exchanges don't offer USD or any foreign currency (EUR, GBP, etc) trading pairs.

I thought I understood how coinmarketcap calculated the price, until I looked at their BTC markets page. I see they're averaging in USD prices of altcoin pairs like TRX/BTC, XRP/BTC, etc as well.

So can someone explain how they determine the USD price (on the BTC markets page) of, for example, TRX/BTC on the Bit-Z exchange without first knowing the actual USD price of BTC? I don't understand where they're getting the USD price of TRX/BTC if its also being factored into the final USD price of BTC as well.

And when I add up the volume percentages in the "Volume (%)" column, it doesn't add up to 100%. More like 94%. Anyone know why that is?

I'm not a mathematician, so maybe there's a simple answer to this.

• This is an interesting question and I've often wondered it myself. You cannot add two unknowns to a system with the same two unknowns and get an improved calculation. For example, does coinmarketcap.com use the price of TRX first to calculate the price of BTC or vise versa? It seems like there must be an ordering or "hierarchy" of the calculations. My guess is that they could do all the USD calculations first, and then go down the "market cap list" or "trade volume list" for the rest of the hierarchy. Commented Apr 1, 2018 at 23:32
• Yea. That's a good guess. Seems like an odd way of doing it. The other strange thing is when I combine the pricing/volume data from all of the markets they display, the final price is always different from what CMC is showing (my price is always lower). At least for BTC and ETH. I tried DASH and my calculation was the same as CMC. So maybe they're using some kind of internal price index for USD pricing on the larger coins. Commented Apr 2, 2018 at 1:31
• Doesn't answer your question, but related: bitrazzi.com/how-coinmarketcap-calculates-bitcoin-price Commented May 22, 2018 at 13:21