The search volume data is based on API information that comes from SEMrush. In very few cases we estimate it ourselves.
In case you see differences between what we show and Keyword Planner from Google or other similar tools here is the explanation:
The search volume is shown for: “keyword” (exact match), NOT for keyword (broad). The keyword planner from Google is not to be used for SEO purposes because it offers keyword info to be used in search advertising, not in organic. Therefore, they show volumes for broad searches and sometimes even similar, because those are SERPs where they could also show your ad, even though it’s not 100% your exact match keyword.