Spreads vary from broker to broker. With forex, you normally look at the most liquid pair to compare the brokers spreads. That’s EURUSD.
Spreads on EURUSD can range from as low as 0.0 up to normally around 2.0. If you see a broker say their average is higher than 2 for EURUSD, I’d probably keep looking. It’s also given as an average, which means you will get both higher and lower than that if you consistently trade EURUSD.
Spreads on other asset classes will range depending on that asset. Cryptocurrencies, for example, are very volatile and not very liquid. Their spread is therefore pretty high.