How we tested
PromptRatio shows the picture each prompt actually produced. To make them, we ran thousands of prompts: most on Google Flow and a smaller set on ChatGPT. Each prompt page carries a badge for the tool it was tested on and lists the exact size of the original picture.
This guide only reports what we saw in our own runs. Both tools change often, so treat the numbers as a snapshot from 2026, not a rule.
The sizes each tool returned
Google Flow gave us three shapes: square 1:1 at 1024 × 1024 pixels, wide 16:9 at 1376 × 768 and tall 9:16 at 768 × 1376. ChatGPT gave us square 1:1 at 1254 × 1254, tall 2:3 at 1024 × 1536 and landscape 3:2 at 1536 × 1024.
That difference matters more than it looks. If you need a 9:16 Reel cover or a phone wallpaper, Flow makes that shape directly; with ChatGPT you get 2:3 and crop the sides. If you need a 2:3 Pinterest pin, ChatGPT fits exactly and Flow's 9:16 needs a small crop at the top and bottom.
Setting the shape
In Google Flow, you choose the ratio in the settings before you generate. In ChatGPT, you ask for the shape in plain words in the same message, such as "make it a tall 2:3 image". On PromptRatio, the help box on every prompt page tells you which of the two applies to that prompt.
In both, writing the shape into the prompt ("A vertical photo of…") helps the tool frame the subject for it.
Working style
ChatGPT works as a conversation. You can ask for changes in plain language ("make the sky darker", "move the cup to the left") and it edits from the previous picture. That makes it good for refining one image step by step, and for prompts that use an uploaded photo of a person.
Google Flow works more like a project board. You send a prompt and get pictures back in a workspace where you can keep, reuse and compare them. That makes it good for making many pictures in a row with the same settings, which is how most of our gallery was produced.
Text in pictures
Short text is where people most often see a difference between tools. In our runs, both tools handled short quoted lines like greetings reasonably often, and both made mistakes on longer text. Whatever the tool, proofread every word before you share.
For prompts that must stay text-free, both tools respected an ending like "No text." well in our runs.
Which one to use
Neither tool is better at everything. Pick the one that fits the shape and the way you like to work.
- You need a tall phone shape or a wide video shape: Google Flow's 9:16 and 16:9.
- You need a Pinterest pin or a classic photo print shape: ChatGPT's 2:3 or 3:2.
- You want to put your own face into the picture: a tool that accepts an uploaded photo with the prompt, such as ChatGPT.
- You want to refine one picture through several small changes: a conversational tool.
- You want many variations quickly with the same settings: a project-style tool like Flow.
Prompts move between tools
A prompt that works in one tool usually works in the other. The subject, setting, light and style words carry over; the result will differ in details, and you may need to change how you set the shape. Each prompt page on PromptRatio answers "Does it work outside…" for exactly this reason.
If a prompt gives a poor result in one tool, try it in the other before rewriting it. Sometimes the tool, not the prompt, is the problem.
Speed and volume
How many pictures you need changes the choice. For one important picture, such as a profile photo or a single post, a slow step-by-step conversation is worth it. For a batch of fifty wallpapers or a full set of festival cards, a tool that keeps your settings and lets you run prompt after prompt saves hours.
Both tools have usage limits that change over time and by plan. Check the current limits in the tool before you plan a large batch, and spread big jobs over several sessions rather than running everything at once.
Limits and rights
Both tools have their own content rules, daily limits and terms for how you may use what they make. Check the current terms of the tool you use before using pictures in ads, products or anything commercial. Our disclaimer page explains how we handle this on PromptRatio.
The "Which model gives what" box on every prompt page repeats the facts above for that prompt: which tool made it, at what size, and what to expect in the other tool.
Tested prompts on this topic
Every prompt in these categories comes with the picture it made, so you can try the ideas above on a prompt that already works: Viral Trends, YouTube Thumbnails, Phone Wallpapers and Instagram Posts. To trim a finished picture to an exact platform size, use the free crop tool.
