 {Bitcoin Amount} * {Exchange Rate} would give you the value of BTC in USD. You'd have to add transaction costs to that, which depend on your exchange.

I will explain how to calculate the value of some amount of bitcoins in terms of USD, but obviously the USD can be replaced by any other currency, and the corresponding exchange rate.

There are three figures involved in this calculation:

The value in USD.

The exchange rate, which gives you the relation of USD to BTC.

The amount of bitcoins.

If you look at the units of the figures, you can figure out the following formula:

value in USD = exchange rate * amount of bitcoins

Or expressed in the units of the terms:

[USD] = [USD/BTC] * [BTC]

As you can see, if you multiply the exchange rate [USD/BTC] with the amount of bitcoins [BTC], the units of the right side will be reduced to [USD], which is what we are looking for.

Example:

We have 0.005 BTC and the exchange rate is 200 USD/BTC.

exchange rate * amount of bitcoins = 200 USD/BTC * 0.005 BTC = 200 USD * 0.005 = 1 USD

You can also turn the equation around to calculate any of the other terms:

To calculate the exchange rate, you take the amount of USD you paid, and divide by the amount of bitcoins you received.

exchange rate = 'value in USD' / 'number of bitcoins'

To calculate the number of bitcoins you might buy with a given amount of USD at a specific exchange rate, you divide the amount of USD by the exchange rate:

number of bitcoins = 'value in USD' / 'exchange rate'

LET US USE NAIRA THIS TIME AROUND FOR THE MATHEMATICAL ILUSTRATION

Let exchange rate = a; Amount in BTC = b; Amount in your native currency e.g Naira = a*b. For instance: You are given exchange rate to be BTC/NGN = 380NGN and you have 0.00548 BTC, The Naira value will be 380 * 0.00548 = 2.0824NGN i.e approximately 2 Naira

Also to calculate the value in Naira '0.04 BTC' will amount to, Just multiply both value of 1 BTC (Bitcoin) = \$50000 (as at today) with 0.04 of of Bitcoin,We have; 0.04 x \$50000 = \$2,000. Then, finally multiply this value by the exchange rate (380NGN). You then finally have; 760,000 NGN

Calculating the price of Bitcoin based on the Bitcoin/USD exchange rate will probably not give you the exact actual cost of Bitcoin in your native currency. The price in your native currency is set by the supply and demand on a local exchange that deals in your own currency. This can vary by as much as 10-30% e.g. South Africa & South Korea at times.

So, you ask, would that means there is a difference in value between BTC/USD, BTC/Native and USD/Native? Yes, that is what arbitrage is based on and many take advantage of the difference to make a profit wherever Btc is valued higher. So bottom line, if you're looking for exact exchange rate look on a local exchange.

Note that;

100 million Satoshis= 1 Bitcoin  i.e

100,000,000 Satoshi = 1 BTC