How important is volume when choosing an exchange?

External question — Personal Finance Stack Exchange Author: ggambetta Original post: https://money.stackexchange.com/questions/28488 License: CC BY-SA 3.0 — https://creativecommons.org/licenses/by-sa/3.0/ Adaptation: HTML converted to plain text; contact email addresses removed. I'm investing some money in ETFs; buy and hold. My local currency is CHF. I have an account in Interactive Brokers. So far I've operated on the London Stock Exchange, which means I have to do a forex operation to buy GBP, which means fees. The ETFs I'm buying are also listed in the Swiss Exchange. I could buy them there and not pay fees. But what worries me is volume: LSE is much higher volume than SIX. I have a vague idea that this affects the spread, but given that I operate infrequently (~once a month) and at low volumes (~tens of shares at a time), would this have any negative effect for me in practice? In general, is there a rule of thumb about the minimum volume where you should operate? Something like "don't trade if the average daily volume is less than 10x your volume" ?