Photoshop script for adding measurements to your mockups, based on Pixel Measure v0.04 by Nikolaj Selvik (https://code.google.com/p/pixelmeasure/)

Pixel Measure.jsx

/*
Photoshop script for adding measurements to your mockups,
based on Pixel Measure v0.04 by Nikolaj Selvik (https://code.google.com/p/pixelmeasure/)

To install: Place in /Applications/Adobe Photoshop CC/Presets/Scripts/ and restart Photoshop.
To use: Draw a rectangle marquee and invoke from File > Scripts > Pixel Measure.

Tips:
- Set your pencil to 1x1 and your foreground color to something visible (e.g., red).
- Set your Measurement Scale (Image > Analysis > Set Measurement Scale).
    For iOS retina, you might use the unit "pt" and set the pixel length to 2 (2px = 1pt @2x).
- Set your DPI scale (Image > Image Size). In the retina example, if 72 is your normal dpi,
    use 144 (72 x 2 = 144).
- Set your ruler to use points.
- Set a keyboard shortcut to invoke the script.

This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
*/

var originalUnit = preferences.rulerUnits;
preferences.rulerUnits = Units.POINTS;
var ratio;

app.displayDialogs = DialogModes.NO;

if(validateState())
{
    app.activeDocument.suspendHistory("Create measurement", "createMeasure();");
}


function validateState()
{
    if (app.documents.length === 0)
    {
        alert("No document open");
        return false;
    } else {
        docRef = app.activeDocument;
        ratio = docRef.measurementScale.pixelLength;
        docRes = docRef.resolution;
    }
     
    if(!hasSelection(app.activeDocument))
    {
        alert("Please make a selection to measure");
        return false;
    }

    if (docRes / ratio !== 72) {
        if (!confirm("Measurement Scale does not match document resolution\rContinue anyway?")) {
            return false;
        }
    }

    try {
        var colorTest = app.foregroundColor;
    } catch(e) {
        alert("Invalid foreground color\r" + e);
        return false;
    }

    return true;
}   


function createMeasure()
{
    var selRef = docRef.selection;
    var mainLayerSet;

    // set density-independent units (dp, pt)
    var measureUnits = docRef.measurementScale.logicalUnits;
    ratio = docRef.measurementScale.pixelLength;
    if(measureUnits == "pixels")
    {
        measureUnits = "px";
    }
    else if(measureUnits == "points")
    {
        measureUnits = "pt";
    }
    
    // =======================================================
    // Create "Pixel Measures" LayerSet if it doesn't already exist
    // =======================================================
    try
    {
        mainLayerSet = docRef.layerSets.getByName("Pixel Measures");
    }
    catch(error)
    {
        mainLayerSet = docRef.layerSets.add();
        mainLayerSet.name = "Pixel Measures";
    }

    // =======================================================
    // Create Measurement LayerSet
    // =======================================================
    var layerSetRef = mainLayerSet.layerSets.add();
    var linesLayerRef = layerSetRef.artLayers.add();

    // =======================================================
    // Draw Lines
    // =======================================================

    // get average color
    var x1 = selRef.bounds[0].value;
    var y1 = selRef.bounds[1].value;
    var x2 = selRef.bounds[2].value;
    var y2 = selRef.bounds[3].value;

    selRef.copy(true);

    var chanRef = docRef.channels.add();
    chanRef.name = "TMP";
    chanRef.kind = ChannelType.SELECTEDAREA;
    selRef.store(docRef.channels.getByName("TMP"), SelectionType.EXTEND);

    docRef.paste();

    var tmpLayer = docRef.activeLayer;
    selRef.load(docRef.channels.getByName("TMP"));
    tmpLayer.applyAverage();
    chanRef.remove();

    selRef.deselect();

    var width = x2 - x1;
    var height = y2 - y1;    
    
    var tmpSampler = docRef.colorSamplers.add(Array(x1 + width/2, y1 + height/2));
    var bgColor = new SolidColor();
    bgColor = tmpSampler.color;
    tmpSampler.remove();

    // figure out what color to use
    var baseColorValue = (bgColor.rgb.red + bgColor.rgb.green + bgColor.rgb.blue) / 3;

    var tmpFgColor = app.foregroundColor;
    
    if(baseColorValue < 192)
    {
        app.foregroundColor.rgb.hexValue = "ffffff";
    }

    var horizontal = width > height;

    if(horizontal)
    {
        drawLine(x1,y1,x1,y1+10/ratio);
        drawLine(x2-1/ratio,y1,x2-1/ratio,y1+10/ratio);
        drawLine(x1,y1+5/ratio,x2-1/ratio,y1+5/ratio);
    }
    else
    {
        drawLine(x1,y1,x1+10/ratio,y1);
        drawLine(x1,y2-1/ratio,x1+10/ratio,y2-1/ratio);
        drawLine(x1+5/ratio,y1,x1+5/ratio,y2-1/ratio);
    }


    // =======================================================
    // Draw Text
    // =======================================================
    var textLayerRef = layerSetRef.artLayers.add();
    textLayerRef.kind = LayerKind.TEXT;
    var textItemRef = textLayerRef.textItem;
    
    textItemRef.size = new UnitValue(5, "pt");
    
    // temporary workaround for text size bug
    if (textItemRef.size.as("pt") != 5) {
        changeTextSize(5*ratio);
    }

    textItemRef.font = "Monaco";
    textItemRef.antiAliasMethod = AntiAlias.NONE;

    var textWidth, textHeight, textX, textY;

    if (horizontal) {
         if (width > 16) {
            textItemRef.contents = width + " " + measureUnits;
         } else {
            textItemRef.contents = width + "\r" + measureUnits;
         }
        textItemRef.justification = Justification.CENTER;
        
        // test position of text and find good offsets
        textWidth = textLayerRef.bounds[2].value - textLayerRef.bounds[0].value;
        textHeight = textLayerRef.bounds[3].value - textLayerRef.bounds[1].value;

        textX = x1 + width/2;
        if (textX - textWidth/2 < 0) {
            textX = 1;
            textItemRef.justification = Justification.LEFT;
        } else if (textX + textWidth/2 > docRef.width.value) {
            textX = docRef.width.value - 1;
            textItemRef.justification = Justification.RIGHT;
        }
    
        textY = y1 + 21/ratio;
        if (textY + 4 > docRef.height.value) {
            textY = y1 - (width > 16 ? 6 : 16)/ratio;
        }
    
        textItemRef.position = Array(Math.floor(textX), Math.floor(textY));
    } else {
        textItemRef.contents = height + " " + measureUnits;
        
        // test position of text and find good offsets
        textWidth = textLayerRef.bounds[2].value - textLayerRef.bounds[0].value;
        textHeight = textLayerRef.bounds[3].value - textLayerRef.bounds[1].value;

        textX = x1 + 15/ratio;
        if (textX + textWidth > docRef.width.value) {
            textX = x1 - 4/ratio;
            textItemRef.justification = Justification.RIGHT;
        }
    
        textY = y1 + 4/ratio + height/2;
    
        textItemRef.position = Array(Math.floor(textX), Math.floor(textY));
    }

    layerSetRef.name = (horizontal ? width : height) + " " + measureUnits;

    textItemRef.color = app.foregroundColor;

    // =======================================================
    // Reset
    // =======================================================
    app.preferences.rulerUnits = originalUnit;
    app.foregroundColor = tmpFgColor;
}


function drawLine(x1,y1,x2,y2)
{
    // Factor in ruler offset, from  http://forums.adobe.com/message/2866222#2866222
    var ref = new ActionReference();
    ref.putEnumerated( charIDToTypeID("Dcmn"), charIDToTypeID("Ordn"), charIDToTypeID("Trgt") ); 
    var desc = executeActionGet(ref);
    var xOffSet = desc.getInteger(stringIDToTypeID('rulerOriginH')) / 65536;
    var yOffSet = desc.getInteger(stringIDToTypeID('rulerOriginV')) / 65536;
    x1 -= xOffSet/ratio;
    x2 -= xOffSet/ratio;
    y1 -= yOffSet/ratio;
    y2 -= yOffSet/ratio;
    
    var pointArray = [];

    var pointA = new PathPointInfo();
    pointA.kind = PointKind.CORNERPOINT;
    pointA.anchor = Array(x1, y1);
    pointA.leftDirection = pointA.anchor;
    pointA.rightDirection = pointA.anchor;
    pointArray.push(pointA);

    var pointB = new PathPointInfo();
    pointB.kind = PointKind.CORNERPOINT;
    pointB.anchor = Array(x2, y2);
    pointB.leftDirection = pointB.anchor;
    pointB.rightDirection = pointB.anchor;
    pointArray.push(pointB);

    var line = new SubPathInfo();
    line.operation = ShapeOperation.SHAPEXOR;
    line.closed = false;
    line.entireSubPath = pointArray;

    var lineSubPathArray = [];
    lineSubPathArray.push(line);

    var linePath = app.activeDocument.pathItems.add("TempPath", lineSubPathArray);
    linePath.strokePath(ToolType.PENCIL, false);
    app.activeDocument.pathItems.removeAll();
}

function hasSelection(doc)
{
    var res = false;
    var as = doc.activeHistoryState;
    doc.selection.deselect();
    if (as != doc.activeHistoryState)
    {
        res = true;
        doc.activeHistoryState = as;
    }
    return res;
}

// Temporary fix for the textItem.size bug: https://forums.adobe.com/message/6804450
// Adapted from https://forums.adobe.com/message/6814050#6814050
function changeTextSize(newSize) {  
    var idsetd = charIDToTypeID( "setd" );  
        var desc23 = new ActionDescriptor();  
        var idnull = charIDToTypeID( "null" );  
            var ref6 = new ActionReference();  
            var idPrpr = charIDToTypeID( "Prpr" );  
            var idTxtS = charIDToTypeID( "TxtS" );  
            ref6.putProperty( idPrpr, idTxtS );  
            var idTxLr = charIDToTypeID( "TxLr" );  
            var idOrdn = charIDToTypeID( "Ordn" );  
            var idTrgt = charIDToTypeID( "Trgt" );  
            ref6.putEnumerated( idTxLr, idOrdn, idTrgt );  
        desc23.putReference( idnull, ref6 );  
        var idT = charIDToTypeID( "T   " );  
            var desc24 = new ActionDescriptor();  
            var idtextOverrideFeatureName = stringIDToTypeID( "textOverrideFeatureName" );  
            desc24.putInteger( idtextOverrideFeatureName, 808465458 );  
            var idtypeStyleOperationType = stringIDToTypeID( "typeStyleOperationType" );  
            desc24.putInteger( idtypeStyleOperationType, 3 );  
            var idSz = charIDToTypeID( "Sz  " );  
            var idPxl = charIDToTypeID( "#Pxl" );  
            desc24.putUnitDouble( idSz, idPxl, newSize );  
        var idTxtS = charIDToTypeID( "TxtS" );  
        desc23.putObject( idT, idTxtS, desc24 );  
    executeAction( idsetd, desc23, DialogModes.NO );  
}  

Does it work with Photoshop CC2015 and 2014