Extending Google's MultiBidder to include Cost Per Conversion Targeting

Over the past 15 years or so of running Google Ads campaigns, I’ve spent huge amounts of time managing campaigns in various ways.

Manual changes, rules, scripts and the MultiBidder all have their advantages and disadvantages and I will generally use a combination of all of those methods in any given campaign. The foundation of most campaigns, though, has become the MultiBidder. Quick primer for those who don’t know:

What is the MultiBidder?

The MultiBidder is a combination of a Google Sheets document and a simple Google Ads script to essentially manage many rules in one place. Let’s say that you’re managing your campaign manually at the moment, adjusting bids for important keywords on a weekly basis: if they’ve got an average position of more than 3 (i.e. not in the top set of ads in most cases) you’re increasing the bid by 5%. Multibidder just allows you to automate that decision, as well as as many other rules as you need to make your campaign run efficiently.

Although not as powerful as custom scripts, Multibidder is my go-to for the foundation of a campaign because it’s very simple to maintain and can be understood by a larger number of colleagues and staff on the client side. It’s also simple to hand over should a client want to continue activity themselves.

The Problem

It’s possible to target many keyword attributes as part of your rules in MultiBidder, like AveragePosition as mentioned as well as things like BounceRate, QualityScore, Ctr. One piece of information you aren’t able to get at, and as such can’t adjust bids due to, is the Cost Per Conversion of a keyword.

Cost per Conversion is an incredibly important metric for a PPC campaign, so I wanted to find a way to adjust our keyword bids based on how successfully that keyword was generating new business for our clients. Achieving a minimal cost per conversion for a given budget means we’re making the most of a client’s budget.

Was it possible to get this data into MultiBidder? A quick Google didn’t give me any readily available solutions, so I looked into creating my own…

The Solution

The solution to this problem hinges on the fact that MultiBidder is a combination of a spreadsheet and a Google Ads script. The script part of the process essentially does this:

1. For each row (rule) in the spreadsheet:
   1. Find all the keywords that match all of the columns (conditions) of the rule, as long as the column/condition matches one of the allowedKeyword Selectors
   2. Apply the designated bid adjustments to each of those keywords

I amended the script which runs the MultiBidder to check whether the condition is based on CostPerConversion, which is not an allowed Keyword Selector. If that’s the case, the script calculates the CostPerConversion from the allowed Keyword attributes Cost and Conversions. It then decides whether to make changes to the current keyword, or skip it as if CostPerConversion was a valid selector.

Case Study: The Replace Base

An online retailer of mobile device repairs and replacement parts

What I ended up with was a version of the MultiBidder which allows me to create rules based around CostPerConversion as if it were an allowed Keyword Selector. That allows us to create automate around a rule like:

“If the cost per conversion for this keyword is above half of the gross profit margin for this product, and the average position is in the top 3, decrease the bid by 10%”

Having this rule, as well as many others, run on a daily basis has resulted in a measurable increase in the efficiency of our campaigns on Google Ads.

Want the amended script? Oh, go on then: MultiBidder Script with CostPerConversion.