Robinhood charges no commission on crypto. It makes its money on the spread, and the size of that spread is published per coin, per side, through its own API - as buy_spread and sell_spread alongside the quote.
The round-trip number
Buying and selling once costs you both sides. Across the coins Robinhood lists, a round trip typically runs around 1.9%, and the range is wide: the thinnest names cost well over 2.5%, the most liquid closer to 1.7%. Stablecoins are the exception at zero.
That figure is worth internalising before any short-horizon strategy. A 1.9% round trip means a trade has to move about two percent in your favour just to break even. Most one-minute candles in Bitcoin move a fraction of that.
Routing changes the arithmetic
Orders can route to market makers - where the cost is that embedded spread - or through exchange routing, which charges an explicit fee instead, tiered by trailing 30-day volume. At the entry tier the two are close to identical. The fee tiers only start to matter above meaningful volume, and the maker rate is roughly half the taker rate, so a resting order costs materially less than a market order.
Why size barely matters
Robinhood's estimated-price endpoint accepts a list of quantities and returns the all-in cost of each. Run it across sizes and the spread barely moves between a small order and a large one. On this venue the markup is the cost, not slippage - which is unusual, and worth knowing if you are used to thinking about market impact.
The Crypto Market Map reads that disclosed markup back for every coin and ranks them, so the cheapest and most expensive things to trade are visible before you trade them.