There are two factors that determine the dollar amount you are risking per pip on a trade.
- The value of a pip for the currency pair in dollar terms.
- The number of lots you are trading of that particular pair.
Many traders who are new to forex don't realize the value of a pip varies from one currency pair to the next.
For example, the value of a pip when trading one standard lot (100,000 units or 100K) of EUR/USD, GBP/USD or AUD/USD is example $10. That's because USD is the counter or quote currency for these pairs.
By contrast, the pip value for EUR/GBP is £10. The pip value for USD/CHF, AUD,CHF and CAD/CHF is 10 Fr. The pip value for USD/JPY, EUR/JPY, and NZD/JPY is ¥1000.
Most trading platforms will automatically convert these pip values into their US dollar equivalent if your account is denominated in USD, but for the sake of simplicity we will give you an example using EUR/USD.
To risk $5 per pip, your trade size on EUR/USD would need to be half of a standard lot (AKA 5 mini lots or 50,000 units or 50K). On your MT4 platform, this may be expressed as 0.50 volume.
To risk 50 cents per pip, your trade size would have to be 0.05 volume (AKA 5 micro lots or 5,000 units or 5K). To risk $50 per pip, your trade size would have to be 5.00 standard lots (AKA 500,000 units or 500K).
In another discussion, @LaughingCharlie made a good point about why you might not want to risk more than 1% of your account on any trade: https://forums.babypips.com/t/how-much-units-cost/112246/4
For your $500 account, that means risking no more than $5, so even a trade size of 5 micro lots might be too big, because it only gives you 10 pips to risk. Consider trading 1 micro lot or 0.01 volume, so you can risk up to 50 pips per trade.