Open Steam and go to your Inventory
Select the game or item category you want to check
Manually add up the market value of each item using the Steam Community Market
Use the Steam Community Market to search each item and note the lowest current price
Multiply item price by quantity for stackable items
Add all item values together for a total estimate
Use a third-party inventory value calculator if you want an automatic total
Log in to the calculator with your Steam account only if you trust the site
Compare results with Steam Market prices for accuracy
Check whether fees are included or excluded in the total
Refresh prices before calculating because market values change often