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

    <schemaVersion>X0203</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2010-02-12</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001121788</issuerCik>
        <issuerName>GARMIN LTD</issuerName>
        <issuerTradingSymbol>GRMN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001483374</rptOwnerCik>
            <rptOwnerName>Biddlecombe Sean</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>LIBERTY HOUSE</rptOwnerStreet1>
            <rptOwnerStreet2>HOUNSDOWN BUSINESS PARK</rptOwnerStreet2>
            <rptOwnerCity>SOUTHAMPTON</rptOwnerCity>
            <rptOwnerState>X0</rptOwnerState>
            <rptOwnerZipCode>SO409LR</rptOwnerZipCode>
            <rptOwnerStateDescription>UNITED KINGDOM</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>General Manager, Garmin Europe</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Shares</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6630</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Employee stock option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.38</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2002-12-21</value>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2011-12-21</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1600</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Employee stock option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>14.90</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2003-12-26</value>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2012-12-26</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1200</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Employee stock option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>27.27</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2006-12-23</value>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2013-12-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>388</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Employee stock option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>27.27</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2004-12-23</value>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <value>2013-12-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3618</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Employee stock option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>19.94</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2005-09-23</value>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2014-09-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5400</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock appreciation right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>21.59</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2006-06-23</value>
                <footnoteId id="F7"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-06-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4700</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock appreciation right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>30.66</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2006-12-16</value>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2015-12-16</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4300</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock appreciation right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>46.15</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2007-06-09</value>
                <footnoteId id="F9"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-06-09</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>6000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock appreciation right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>51.07</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2007-12-05</value>
                <footnoteId id="F10"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-12-05</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock appreciation right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>63.31</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2008-06-08</value>
                <footnoteId id="F11"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-06-08</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock appreciation right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>105.33</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2008-12-04</value>
                <footnoteId id="F12"/>
            </exerciseDate>
            <expirationDate>
                <value>2017-12-04</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Stock appreciation right</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>50.97</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <value>2009-06-06</value>
                <footnoteId id="F13"/>
            </exerciseDate>
            <expirationDate>
                <value>2018-06-06</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>5000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The number of shares reported includes: (1) 3,000 Common Shares that were acquired on December 12, 2008 pursuant to a grant of restricted stock units under the Garmin Ltd. 2005 Equity Incentive Plan, which award vests in five equal annual installments beginning on December 12, 2009 (750 of the 3,750 Common Shares granted under the award vested on December 12, 2009, leaving 3,000 unvested Common Shares as of the date of this report); (2) 1,580 Common Shares that were acquired on December 11, 2009 pursuant to a grant of restricted stock units under the Garmin Ltd. 2005 Equity Incentive Plan, which award vests in five equal annual installments beginning on December 11, 2010.</footnote>
        <footnote id="F2">The option vested in five equal annual installments beginning on December 21, 2002.</footnote>
        <footnote id="F3">The option vested in five equal annual installments beginning on December 26, 2003.</footnote>
        <footnote id="F4">Sixty percent of the options vested on December 23, 2006, and twenty percent of the options vested on each of December 23, 2007 and December 23, 2008.</footnote>
        <footnote id="F5">The option vested in five equal annual installments beginning on December 23, 2004.</footnote>
        <footnote id="F6">The option vested in five equal annual installments beginning on September 23, 2005.</footnote>
        <footnote id="F7">The right vests in five equal annual installments beginning on June 23, 2006.</footnote>
        <footnote id="F8">The right vests in five equal annual installments beginning on December 16, 2006.</footnote>
        <footnote id="F9">The right vests in five equal annual installments beginning on June 9, 2007.</footnote>
        <footnote id="F10">The right vests in five equal annual installments beginning on December 5, 2007.</footnote>
        <footnote id="F11">The right vests in five equal annual installments beginning on June 8, 2008.</footnote>
        <footnote id="F12">The right vests in five equal annual installments beginning on December 4, 2008.</footnote>
        <footnote id="F13">The right vests in five equal annual installments beginning on June 6, 2009.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Joshua H. Maxfield, Attorney-in-Fact</signatureName>
        <signatureDate>2010-02-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
