<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-02-29</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001396033</issuerCik>
        <issuerName>Lumber Liquidators Holdings, Inc.</issuerName>
        <issuerTradingSymbol>LL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001417490</rptOwnerCik>
            <rptOwnerName>SULLIVAN THOMAS D</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3000 JOHN DEERE ROAD</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>TOANO</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>23168</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman of the Board; Founder</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-02-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>75513</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.1089</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1312198</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-03-01</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>76200</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>22.3449</value>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1235998</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Average weighed sale price for prices ranging from $22.00 to $22.28.  100 shares were sold at the following prices: $22.0419 and $22.0619; 164 shares were sold at $22.0829 per share; 200 shares were sold at $22.19 per share; 300 shares were sold at $22.27 per share; 400 shares were sold at the following prices: $22.0019, $22.0719, $22.0919, $22.2019, $22.23, $22.2419 and $22.2519; 600 shares were sold at the following prices: $22.0119, $22.0519, $22.0819, $22.2219, $22.2319, $22.2619 and $22.2719; 800 shares were sold at $22.28 per share; 836 shares were sold at $22.15 per share; 900 shares were sold at $22.09 per share; 1,000 shares were sold at $22.1919 per share; 1,100 shares were sold at $22.21 per share; 1,200 shares were sold at $22.24 per share (Continued in Footnote 2).</footnote>
        <footnote id="F2">(Continued from Footnote 1) 1,400 shares were sold at the following prices: $22.07 and $22.26; 1,600 shares were sold at $22.06 per share; 1,800 shares were sold at $22.03 per share; 1,900 shares were sold at $22.08 per share; 2,200 shares were sold at $22.10 per share; 2,345 shares were sold at $22.01 per share; 2,375 shares were sold at $22.02 per share; 3,400 shares were sold at $22.22 per share; 3,700 shares were sold at $22.04 per share; 4,600 shares were sold at $22.20 per share; 9,400 shares were sold at $22.25 per share; 12,000 shares were sold at $22.05 per share; and 13,693 shares were sold at $22.00 per share.</footnote>
        <footnote id="F3">Average weighted sale price for prices ranging from $22.30 to $22.4119.  2 shares were sold at $22.3750 per share; 100 shares were sold at $22.3150 per share; 400 shares were sold at each of the following prices: $22.3019, $22.3519 and $22.36; 600 shares were sold at $22.3819 per share; 700 shares were sold at $22.34 per share; 800 shares were sold at each of the following prices: $22.3319, $22.3619, $22.41 and $22.4119; 1,000 shares were sold at $22.3719 per share; 1,400 shares were sold at $22.3219 per share; 1,700 shares were sold at $22.38 per share; 2,200 shares were sold at $22.32 per share; 2,600 shares were sold at $22.39 per share; 4,000 shares were sold at $22.31 per share; 4,400 shares were sold at $22.4019 per share; 5,515 shares were sold at $22.37 per share; 7,000 shares were sold at $22.33 per share; 7,800 shares were sold at $22.40 per share; 13,283 shares were sold at $22.35 per share; and  19,500 shares were sold at $22.30 per share.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>E. Livingston B. Haskell, Power-of-Attorney</signatureName>
        <signatureDate>2012-03-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
