How to Estimate a Minimum Swap Size for Each Asset Pair

Estimate a route’s minimum size by finding the amount at which its fees stop consuming too much of the input, then confirm it with a live quote. There is no single minimum that works for every asset pair. The source chain, destination chain, pool depth and current network fees all affect the result.

THORChain’s developer docs describe separate costs for sending funds in, using pool liquidity and sending the output asset. A cross-chain swap may use two pools, so both the route and the destination matter. For a fuller account of wallet setup and the swap flow, see thor swap.

What costs set the minimum route size?

The minimum is the point where the expected output still makes sense after fees. Start with the source-chain fee, which your wallet charges to send the deposit. Then account for the pool’s liquidity fee, the destination-chain outbound fee and any optional interface fee. A failed swap can also cost money: THORChain’s docs say a refund may deduct an outbound fee on the source chain.

Fixed fees matter more on a small trade. If a route costs the equivalent of $5 to send and deliver funds, that cost is 5% of a $100 input but 0.5% of a $1,000 input. The percentages are examples; actual fees change with the chains and network conditions.

How does the asset pair change the estimate?

Each pair has its own fee mix and liquidity, so estimate the route for the exact assets you plan to swap. A pair that ends on a chain with costly transactions can have a higher practical floor than one with cheaper delivery. Thin pools also make a given trade larger relative to available liquidity, which can increase price impact, the change in price caused by the trade.

Use the same input asset and destination asset when comparing quotes. If the interface lets you choose a route or swap mode, compare the expected output and total fees, not just the headline rate. A slower, divided swap may reduce price impact, but it does not make fixed network costs disappear.

How can you check a sensible minimum?

Get a fresh quote for the pair and treat its suggested minimum as a starting point, not a promise that the trade is worthwhile. THORChain’s Swap Quote endpoint includes recommended_min_amount_in, an estimate of the input needed to cover minimum fees. The docs say it can change with network settings and conditions.

Before sending, compare the quote at your intended size with the smallest quoted size that clears fees. Check these items:

• Input-chain fee shown by your wallet.
• Output-chain fee and any affiliate fee in the quote.
• Expected output after fees, compared with your own minimum acceptable amount.
• Price impact for the route at that size.

Use a buffer if fees can rise before the transaction is processed, and refresh the quote before signing. The practical minimum for an asset pair is the smallest size that clears the fee floor and still meets your output target. If the quote cannot show that clearly, wait or choose a larger input.