Which is better for framing and decking?

The DCS578. Its 7-1/4-inch blade cuts 2-9/16 inches deep at 90 degrees, so it handles 2x lumber in one pass, and the electric brake speeds up repeated cuts. The DCS391B works for lighter framing but tops out at 2-1/8 inches.

Do I need FlexVolt batteries for the DCS578?

Yes. It is a 60V MAX bare tool, so you need a DeWalt FlexVolt battery and charger, sold separately. The DCS391B runs on standard 20V MAX packs, which many DeWalt owners already have.

Is the DCS578 worth the extra $86?

Only if you cut thick stock often or already own FlexVolt batteries. At $184.99 at Walmart versus $99.00 at Amazon as of November 4, 2026, the DCS391B is the better value for occasional home and trim work.

Which is lighter to use overhead?

They are close: 8.4 lb for the DCS391B and 8.2 lb for the DCS578, both bare tool. The smaller 6-1/2-inch body of the DCS391B feels easier to control on a ladder or roof.

Can either saw cut metal or masonry?

Neither is designed for it. Both list wood as the material, though the DCS578 also names OSB and OSB subfloor. Use a dedicated metal or masonry saw for those materials.

Which has better safety features?

The DCS578, because it has an electric brake that stops the blade quickly after you release the trigger. The DCS391B has a spindle lock for blade changes but no brake.

DeWalt 20V MAX Circular Saw dcs391b vs DeWalt FlexVolt 60V Max Circular Saw DCS578

Buy the DCS391B if you want a light 6-1/2-inch saw for framing, decking and trim on a budget. Buy the DCS578 if you already own DeWalt FlexVolt batteries or need to cut 2x stock at depth and bevels up to 57 degrees. The DCS391B is $99.00 at Amazon as of November 4, 2026; the DCS578 is $184.99 at Walmart as of the same date. That is about $86 more for the bigger blade, more power and an electric brake.

Today the DeWalt 20V MAX Circular Saw dcs391b costs $85.99 less at its best price.

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