AdWords lets you set daily budgets for your campaigns with the flexibility to change them at any time. Your ad spend budget is the money you’ve set to spend to bid on ads. You choose a daily budget for each campaign based on your advertising goals at an amount you’re comfortable spending each day. That budget will vary greatly depending on the size of your business and whether you are running local or national campaigns.
With automatic bidding, AdWords lets you bid based on a target return on ad spend (ROAS). It predicts future conversions and associated values using reported conversion values, which you report through conversion tracking. AdWords sets maximum cost-per-click bids to maximize your conversion value while trying to achieve an average return on ad spend (ROAS) equal to your target. You get more conversion value at the target you set, but this still needs to be monitored and managed.