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Comment by leeoniya | Hacker News Reader

> 100ms added latency can cost you 7-8% in conversions

i hear this metric (or something equally absurd) cited frequently and have never seen it to be true in my own experience.

i guess if you have to load a product page with 100 images (or assets) and each has 100ms network latency, then it will add up to much more than that. but 100ms for a single interaction or network request (e.g. process payment POST) is not going to move the needle on conversions. 100ms will feel instantaneous to 97% of users, and more than satisfactory for the remaining 3%.

(i say this as someone who profiles aggressively and strives to optimize every stray 5ms in JS and every 1kb over the wire)

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I did a study on this (N>100m) at a previous employer who had quite a lot of e-commerce traffic.

It's sort of true but also a massive over simplification. The relationship between conversion and speed is not linear. Some people are beyond help, and others already have it so good they only notice the most extreme degradation in performance.

It's also hard to isolate confounding factors like users who have fast infrastructure tend to be rich and rich people buy more stuff. Making pages load faster doesn't give them more money to buy stuff.

Overall faster is definitely better but the specific magnitude will depend on your customer demographics. In our case the Amazon 100ms saved = 1% more sales was close enough for a rule of thumb.

I could see the 100ms/7% impact coming into play for a super impulsive shopper going from page to page compulsively until they pull the trigger on a product. I wouldn't be surprised if that was a lot of Amazon's business—people buying things they had not set out to buy.

Makes less sense the smaller an e-shop gets since the consumer already needed intent to shop there. If I know I already want product X on Shop Y today, 10 second load times are rather inconsequential.

I've been thinking about that a lot lately. I have a medium-sized e-commerce. We sell hyper-customized products and, to be honest, the site's overall performance is not good. But when I looked into other stores in the same niche as ours, who are making a lot more money than us, I saw that their performance wasn't better than ours. I don't think people shop impulsively in our store because they have to customize the product and then make sure the customization is correct (it's a pretty complex customization). I believe that because the journey to checkout is so long and requires so much attention, the customers just don't give up due to high latency or slow responsiveness overall.

I've worked in e-commerce for a while and have heard similar stated from time to time and seemed like someone was trying to fit a linear line over what's almost certainly an s-curve distribution.

At lower latencies no one is going to leave your site because it takes 1200ms instead of 1000ms to fully load a page. But at some point almost everyone is going to leave your site rather than wait.

I also find these stats really confusing because whenever someone talks to me about site performance they're always talking about a different metric (server response time, first paint, time to interactive, etc). If you're first paint is quick then users aren't going to care if content half way off the page doesn't load instantly.

I've always tried to focus on how fast things feel rather than worrying too much about specific metrics. If you can just get something (ideally the important bit(s)) to load really fast a site can feel extremely fast even if it's mostly just an illusion. Users like to click things and see stuff happening. It's things like reloading the page when adding items to cart then making them wait on a white screen for multiple that increases bounce times as abandoned carts in my experience. Making add to cart buttons an ajax request probably helps far more than making the page load 200ms faster.

Also, this can make me bounce: ,,payment failed, please start again with an empty shopping cart''. It happens on quite many webshops.

I guess that's not really performance, but I agree that UX is one of those things that can subtlety annoy someone enough that they'll just give up and go elsewhere. That's a pretty extreme example, but even simple things like asking the user for too much information over too many pages at checkout can dramatically increase bounce rate. If a user can't land on your site, find what they're looking for then checkout within a few minutes, something is wrong.

On payment failures, an interesting solution an ecommerce I used to work for came up with was just to place the order on payment failure. They figured it was better just to send out an email after the fact asking them to try again and if that failed they could call and take the payment over the phone if need be. We targeted an older demographic and sold fairly pricey products though. I guess that model wouldn't work so well if you're selling $10 tshirts. I believe Amazon does something similar. I know they've sent me emails in the past letting me know my payment failed after placing an order.

I think that particular metric (or one very like it) was originally about… Amazon.com.

So, y’know, maybe a slightly different ballgame.

maybe there was more nuance to that statement, but i never bought it at face value, even then.

Google did a large study. If your page load is 5s then adding 100ms does not matter. I got the raw data from them and it mattered in the curve closing in on the whole page taking 200ms or so. It’s level, and then around 2.5s, each 100ms made more and more of a difference.

Yeah I think the main thing for a website to hold on to users it should at least be interactive and responsive quickly (with clear loading indicators) even if it is taking a while to load everything on the page. If a page looks like it is stuck or feels like it is stuck then I am likely to abandon it. But if it has clear indicators and animations to indicate something is happening, I will be more patient with it.

I think if frame it as, “each 100ms you shave off a critical consumer shopping checkout flow page increases conversions by X%” it starts to seem more defensible.

Agreed that in the general case 100ms to full paint (with interactivity not far behind) is really good.

Doesn't really matter if the relationship isn't linear like that. I suspect it's more likely conversions start to drop off after certain thresholds are met e.g. 3 seconds causes conversions to drop by 5%, 20 seconds causes them to drop by 30%.

Just averaging out those numbers could result in engineering time being wasted chasing rapidly diminishing returns, if the site is already below one of those thresholds.

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