SUM: Single Usability Metric

Jeff Sauro, PhD

SUM is a standardized, summated and single usability metric. It was developed to represent the majority of variation in four common usability metrics used in summative usability tests: task completion rates, task time, satisfaction and error counts.

The theoretical foundations of SUM are based on a paper presented at CHI 2005 entitled “A Method to Standardize Usability Metrics into a Single Score.” Sauro and Kindlund.

Usability ScoreCard
The UsabilityScorecard web-application will take raw usability metrics (completion, time, sat, errors and clicks) and calculate confidence intervals and graph the results automatically. You can also combine any combination of the metrics into a 2, 3 or 4 measure combined score. Data can be imported from Excel (.csv) and exported to Word(.rtf).

Note, the Usability Scorecard app has been decommissioned but the functionality is available in the MUIQ platform


SUM Calculator


The SUM calculator will take raw usability metrics and convert them into a SUM score with confidence intervals. The analyst needs to provide the raw metrics on a task-by-task basis and know the opportunity for errors (if measuring errors). SUM will automatically calculate the maximum acceptable task time, or it can be provided. This calculator can combine 3 or 4 measures (time, ease, completion and optionally errors).

Download the SUM Calculator


Updated 10/21/2019

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