Ratio is beverage weight divided by dry dose. It changes concentration and extraction balance quickly, so ratio decisions should be made with shot time context, not in isolation.
Translate ratio into grams fast
Common examples: 18g dose at 1:2 is 36g out, 20g dose at 1:2 is 40g out, and 22g dose at 1:2 is 44g out.
For a longer profile, 18g at 1:2.5 is 45g out. For a shorter profile, 18g at 1:1.8 is about 32g out.
Decide whether to change grind or ratio first
If shot time is outside 25 to 35 seconds by more than 6 seconds, adjust grind first and hold ratio constant for the next shot.
If shot time is already in band and flavor is off, adjust ratio by 1 to 2g yield instead of moving grind immediately.
Use practical ratio bands by roast style
Medium roasts often start near 1:2. Light roasts often benefit from 1:2.3 to 1:2.8. Dark roasts often land closer to 1:1.8 to 1:2.1.
Use these as starting bands, then tune by taste and repeatability because grinder burr geometry and water chemistry still shift outcomes.