We preferred those that could fax more formats, so you don’t have to convert files before sending them.

A variety of supported file formats: Some fax services support only one or two file types, such as PDF and TIFF.We knocked off points for fax services that buried important settings or required us to click through multiple screens to send a fax. Cover-page templates and the option to save fax numbers in an address book also simplified faxing for us.

We appreciated when services made uploading a file as simple as dragging and dropping or connecting your cloud-storage account.

User-friendly interface and convenient fax features: Sending a fax should be as easy as sending an email.

The 25-page fax we used was a version of tax instructions from the IRS (PDF), with different type sizes, tables, and simple graphics.) To test fax receiving, we faxed our top contenders using HP’s fax testing service and also faxed twice from a laptop with a fax modem connected to a VoIP line. (Specifically, we used the AIIM scanner test chart (PDF) for the single-page tests to gauge fax resolution, because it offers a variety of grayscale details that serve as good stand-ins for text, charts, and other graphics. For each service we considered, we sent three test faxes to a virtual Kall8 phone number: a one-page PDF, a one-page DOC, and a 25-page PDF.

Fax reliability and quality: There’s no point in trying to send a fax if it’s not going to be delivered or the quality is so poor that you have to resend it.

We avoided services with confusing price tiers, sign-up fees, or extra charges for features that a freelancer or small-business owner would regularly need to access. For professional use, we focused on options that had straightforward subscription pricing.

Free faxing or low fees: For occasional faxing, we sought out the services that let you fax for free or that charged no more than a one-time $1 to $2 fee to send a long document.

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