Free tools
Free CRO calculators
Plan a test, check the result, and size the revenue. Every calculator runs in your browser, needs no signup, and shows the formula it uses.
Plan a test
Sample size calculator
How many visitors per variant you need to detect a given lift at your chosen confidence and power.
Open calculatorTest duration calculator
How many days a test should run, given your traffic, baseline rate, and the lift you want to detect.
Open calculatorMDE calculator
The smallest lift a test can reliably detect, given your traffic and how long you can run it.
Open calculatorMeasure performance
Turn a single test into a running program
These calculators size a single test. Spar runs the whole loop: it audits your storefront, ranks the gaps by revenue impact, drafts the variations, and measures the result. Start a 14-day free trial.
Keep exploring
More from Spar
Compare Spar
See how Spar lines up against VWO, Optimizely, and the Shopify-native testing tools.
Explore
Solutions
How Spar fits founders, in-house ecommerce teams, agencies, and Shopify Plus brands.
Explore
Resources
Neutral tool comparisons and curated roundups for Shopify CRO and experimentation.
Explore
Guides
Practical playbooks for prioritizing tests and running Shopify conversion optimization.
Explore