<SEC-DOCUMENT>0001170010-19-000074.txt : 20190503
<SEC-HEADER>0001170010-19-000074.hdr.sgml : 20190503
<ACCEPTANCE-DATETIME>20190503162728
ACCESSION NUMBER:		0001170010-19-000074
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20190501
FILED AS OF DATE:		20190503
DATE AS OF CHANGE:		20190503

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Lyski James
		CENTRAL INDEX KEY:			0001376853

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-31420
		FILM NUMBER:		19796582

	MAIL ADDRESS:	
		STREET 1:		ONE NATIONWIDE PLAZA 1-38-06
		CITY:			COLUMBUS
		STATE:			OH
		ZIP:			43215

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CARMAX INC
		CENTRAL INDEX KEY:			0001170010
		STANDARD INDUSTRIAL CLASSIFICATION:	RETAIL-AUTO DEALERS & GASOLINE STATIONS [5500]
		IRS NUMBER:				541821055
		STATE OF INCORPORATION:			VA
		FISCAL YEAR END:			0228

	BUSINESS ADDRESS:	
		STREET 1:		12800 TUCKAHOE CREEK PARKWAY
		CITY:			RICHMOND
		STATE:			VA
		ZIP:			23238
		BUSINESS PHONE:		(804) 747-0422

	MAIL ADDRESS:	
		STREET 1:		12800 TUCKAHOE CREEK PARKWAY
		CITY:			RICHMOND
		STATE:			VA
		ZIP:			23238
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_155691523438868.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2019-05-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001170010</issuerCik>
        <issuerName>CARMAX INC</issuerName>
        <issuerTradingSymbol>KMX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001376853</rptOwnerCik>
            <rptOwnerName>Lyski James</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>12800 TUCKAHOE CREEK PARKWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>RICHMOND</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>23238</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP &amp; Chief Marketing Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (Right to Buy)</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>78.61</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-05-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>49136</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2026-05-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>49136.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>49136</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The stock options were granted in tandem with stock appreciation rights (SARS). Accordingly, the exercise of one results in the surrender to the Company of the other. The SARS become exercisable only following a change in control of the Company as set forth in the Company's 2002 Stock Incentive Plan, as amended and restated. Once exercisable, the SARS would entitle the Reporting Person to receive the cash value of the options in lieu of exercising the options.</footnote>
        <footnote id="F2">The stock options become exercisable with respect to one-fourth of the underlying shares of Common Stock on each of May 1, 2020, May 1, 2021, May 1, 2022 and May 1, 2023.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Christine Carter, attorney-in-fact</signatureName>
        <signatureDate>2019-05-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
