<p:knob>

Podemos darle un tamaño con las propiedades

 height="70" width="70"

<b:row>

                <b:column span="2">
                    <h4><p:outputLabel value="#{msg['label.totalsolicitado']}"/></h4>
                    <div class="knob-container  ui-corner-all">
                        <p:knob value="#{dashboardIndexController.totalSolicitado}" max="#{dashboardIndexController.totalSolicitado}"
                                disabled="true" 
                                height="70" width="70"
                                foregroundColor="black" backgroundColor="#00000"
                                />
                    </div>
                </b:column>
                <b:column span="2">
                    <h4><p:outputLabel value="#{msg['label.totalaprobado']}"/></h4>
                    <div class="knob-container  ui-corner-all">
                        <p:knob value="#{dashboardIndexController.totalAprobado}" max="#{dashboardIndexController.totalAprobado}"
                                disabled="true"
                                height="70" width="70"
                                foregroundColor="green" backgroundColor="#00000"
                                />
                    </div>
                </b:column>

                <b:column span="2">
                    <h4><p:outputLabel value="#{msg['label.totalrechazado']}"/></h4>
                    <div class="knob-container  ui-corner-all">
                        <p:knob value="#{dashboardIndexController.totalRechazado}" max="#{dashboardIndexController.totalRechazado}"
                                disabled="true"
                                height="70" width="70"
                                foregroundColor="red" backgroundColor="#00000"
                                />
                    </div>
                </b:column>
                 <b:column span="2">
                    <h4><p:outputLabel value="#{msg['label.totalcancelado']}"/></h4>
                    <div class="knob-container  ui-corner-all">
                        <p:knob value="#{dashboardIndexController.totalCancelado}" max="#{dashboardIndexController.totalCancelado}"
                                disabled="true"
                                height="70" width="70"
                                foregroundColor="blue" backgroundColor="#00000"
                                />
                    </div>
                </b:column>


                <b:column span="2">
                    <h4><p:outputLabel value="#{msg['label.totales']}"/></h4>
                    <div class="knob-container  ui-corner-all">
                        <p:knob value="#{dashboardIndexController.totales}" max="#{dashboardIndexController.totales}"
                                disabled="true"
                                height="70" width="70"
                                foregroundColor="brown" backgroundColor="#00000"
                                />
                    </div>
                </b:column>
                <b:column span="2">

                </b:column>
                </b:row>