There are apps which can do a one page checkout, but you will not find it in the Shopify app store. One example is here.
Another option is to go for Shopify Plus, which lets you modify the checkout page.
To clarify on the post above, Shopify Plus won't enable a one page checkout. The steps must still be honoured as the calculation of tax and shipping rely on them. Some modifications to template can certainly emulate something that appears like one but you must be ready to support that kind of change,
For my own learning, why do you need a one page checkout? I'm always hunting for metrics that show it's better, or if there's certain verticals that it works better in. Reducing cognitive overload with multiple steps is my preference.
Yeah I understand the calculation of taxes and address, and i think if my customers created an account it would probably make it easier to order next time. But the reason i want a one page checkout is because it makes an easier conversion. I know from personal experience i may really like a product i found online, but depending on my mood i may not feel like jumping through all the hoops to order. i just don't see what is difficult about putting in all relevant customer information on one page, that is name and address, payment method, then click next to verify and complete order on next page. maybe there is a reason is is divided into 4 sections??
3dcart has a one-page checkout option, "out-of-the-box". I think it has to do with validation, and it's probably a sort of precedent that was set in online shopping checkout design. One-page checkout is the best option for conversion, I think. Faster, easier, and all the information on one page. Customer doesn't have to take multiple screenshots for evidence troubleshooting. There's a number of positives.
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