---
title: Calculating Actual Size of Glass in Sash and Direct Glazed Units
description: Setting up sectional details in order to get accurate glass sizes is not self explanatory. This document lists DrawingBoard properties involved and explains the logic behind actual size calculation. S
---

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# Calculating Actual Size of Glass in Sash and Direct Glazed Units

## Learn how to configure drawing properties for accurate glass sizes in sash and direct glazed units.

### **Key Points: Actual Size Calculation for Glass in Sash**

**1. Understanding information used for the calculation**  
The system uses **three key details** for actual glass size calculation in all types of sashes, for example, sliding, casement, door:

**a. Glass sightline** - Calculated by DrawingBoard using overall frame sizes and sectional details configured

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXeyt-hCi0wYD23SkFMF1teJTZ30SHZQExIGFy3DH2efrORJAog3eBn4vMpVaw9ayrC3HYUmPrUq2tgali6D116SnT_YulFrYRVjw4tDUKZ-2my0ijWDMCSH2N42P9J5PNu0xDVQ-DWmh7OEYVXI-BZIXdA?key=mfTC2E-qiPvm5qpo0nw8ow)  
  
**b. Glazing rebate width** - Set on the default value page. The system uses **five defaults** based on drawing details. This value is the amount taken off from sash stile to accommodate glass unit and tolerance

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXfIJ6UBZpuzccPjQfTxM9Nvf-F7wVBXFe5BwSJ7upsl78b7N1oQ5Db4RRZ2Sd0-nME5ekLypO7ZvExM6lvSIjJTcsazznliAQA3fWu7E1G5EunsJkcWbvTduL3ZjSWhKZjLIBRJedymQSAuaXQUBdVeMluV?key=mfTC2E-qiPvm5qpo0nw8ow)

**c. Glazing tolerance** - Set on the default value page, providing **four defaults**

***Note:** This value is the gap between glazing rebate and edge of glass unit on one side of the glass. If is it set to 0, it will default to 2.5 .*

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXeTpqwqEtYwN-NPl4DK3Omg8hy-EcE68RSDgvDyrETDrchMqfnEvN0zmQxtHFoslEO-ujkyO2e7kYJbiKFUAl1Z7cwutv77ZhXu37XL3RvpTy1FWHA7OUN48g7-xG4VY8xY3wvbu_exW1MzAxD0dIY1xXTT?key=mfTC2E-qiPvm5qpo0nw8ow)

**2. Understanding calculation of actual glass size  
Glass hidden in rebate** is calculated from glazing rebate width and glazing tolerance:  
*Glass Hidden in Rebate = Glazing Rebate Width - Glazing Tolerance*

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXfQZCQPyT8UfJHjo9cb5uDGjaPUpPUUEelo2Tj3s_XMJhgfERo6XtKrcle8mjeUNEfgjSTFQhoXtw8nJbQZr-ktzdiMfKDhqYEe34AjvCzQFPOe1ETwpzUIUmS9DlKxyS2kmoidQNr5U7HVfMHtDAYXRNLA?key=mfTC2E-qiPvm5qpo0nw8ow)

Using these details the actual sizes for the glass is calculated as follows:  
*Glass Actual Width **=** Sightline Width + 2 x (Glazing Rebate Width - Glazing Tolerance)*

 

### **Key Points: Actual Size Calculation for Direct Glazed Units**

**1. Understanding information used for the calculation**  
The system uses **four key details** for the actual glass size calculation for direct glazed units (DirGUs):

**a. DirGU stop size** - Set on the default value page

***Note:** This value is the size of the stop around the direct glazed unit. Distance between profiled frame and glass sightline. If not set, system will use 15 mm.*

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXetMYhmyrYhMkDcvb5cEMAI0x2hN5oQAwaAPnq1RgO-llbEEsRgyo_3UBi_0HlD69Grpm0RVCKp9GnUwAJfOqOVvtbeOwNwqtKSOG_5b8mpYGVqm1FhbusugHQDyLW-Jhyi9ILjr332cx9IJxsV5xVTYl7d?key=mfTC2E-qiPvm5qpo0nw8ow)

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXc-TG5A_RqsYYeeGYfq2IvlRrji7YFJfS7INVy09wYE7nIJ2DbK10KdEYt93TdKhva3gfTjawulZzRF1LkoPETNdyThvnUc6FvVu1d0AxXh2XzA_eRLCS2aKYP12Jm6nlC_v-0Aal5jEsVJ2EqVnrD-cfQ?key=mfTC2E-qiPvm5qpo0nw8ow)

**b. Glass sightline** - Calculated by DrawingBoard as follows:  
*Sightline Width = Overall Frame Width - (2 x (Profiled Frame Jamb + DirGu Stop Size))*

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXd2Jn592qeq3ixAbkZ1edcexROttPuZGAuZl70wsF0mHTHVrHiZjbO-7xrsRyEQRowE8h_GgJ5C2btMUhwsiV2f8Rqv-Z8wLTwmoUlDB30ksKH22XZt2xyFNXEgshJZ5T99FycTVFw5gV_QgoIsMpLYymac?key=mfTC2E-qiPvm5qpo0nw8ow)

**c. Glazing rebate width** - Set on the default value page

***Note:** The system uses five defaults based on drawing details.* 

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXeodi731CGxL2Hl_blWoAragOhJYJlhQyTOqIGLk5A2-5LKpltDPCiMuo0BkknhCP8sOwNVdBoMpsDzxGzmf6-R3z3oncDX-NXkCJVa6DYVLc_F-mZIxxVbvfVsW3WPkr7LZK_BCErCKCIiSxPpqCbKvCXD?key=mfTC2E-qiPvm5qpo0nw8ow)

**d. Glazing tolerance** - Set on the default value page, providing **four defaults**

***Note:** This value is the gap between glazing rebate and edge of glass unit on one side of the glass.*

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXeEAexiRk64xGDmsJnIORV61GpHmKA3dpJ_eiO70sESOm_ARuDOHJOBahbpd54m70VTpIAY1OGFoJwzq216sK84pWbE8kTb-ohX9y6xz2IPp7NecBxtGsmLWwsLNWUT2x5ULshpmeHVHx3VA9ms8ISUMscS?key=mfTC2E-qiPvm5qpo0nw8ow)

 

**2. Understanding calculation of actual glass size  
Glass hidden in rebate** is calculated from glazing rebate width and glazing tolerance:  
*Glass Hidden in Rebate = Glazing Rebate Width - Glazing Tolerance*

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXfAm5s-w3q99RVLvD6fseak6GfrBKNjoiiiJ3hfJmKvUi-3Hy5lfKhqP4p2kg-gYq8O5GorybEZ06G8QLUjgkUz6XzuExKH5zmaxfcRhLVAEZPacNIKB1W7oFWKs1bZnGe-kx0Hey6QQmHcOmC_i3Xkwq8-?key=mfTC2E-qiPvm5qpo0nw8ow)

Using these details the actual sizes for the glass is calculated as follows:  
*Glass Actual Width **=** Sightline Width + 2 x (Glazing Rebate Width - Glazing Tolerance)*

### **Key Points:  Rails for Direct Glazed Units**

**1. DirGU edge touching a rail**  
Direct glazed units can also have top and bottom rails. If an **edge** of a **DirGU** touches a **rail**, for that edge, the system will use **sash rebate and tolerance**. 

**2. DirGU edge touching the frame**  
Direct glazed units can also have top and bottom rails.**If the edge** of a **DirGU** touches the **frame,** not a rail, the system will use **DirGU rebate and tolerance**.

![](https://lh7-rt.googleusercontent.com/docsz/AD_4nXd-QSJWkUEtFi-yq7uEBMycBbwexhRseq4oEXD8ZXvXqjll6msQEdYHuCNf2nYQKGftr1CNGklRPg0Iy75UnnqYT5h9oh8LvtT6Mf7bkv_thzrxVa65BVwpy2uutuTyyQ-MAZgf67QD021Pz4b9tgr3MnAE?key=mfTC2E-qiPvm5qpo0nw8ow)

### **Key Points: Glazing Bars (GB)**

![](https://knowledgehub.endtoendit.com/hs-fs/hubfs/image-png-Aug-01-2025-10-37-51-5161-AM.png?width=620&height=357&name=image-png-Aug-01-2025-10-37-51-5161-AM.png)

|  | **Single Glazing** | **Double / Triple Glazing** |
| --- | --- | --- |
| **Bonded-on Bars** | Rare, mainly used with laminated glass | Most common for sealed units |
| **Georgian Bars** | Traditional window manufacturing | Individual sealed units, called heritage units in integrate |

**1. Bonded-on or Astragal Bars**  
Bonded-on bars do not affect glass sizes.

**2. Georgian or True Bars**  
When actual sizes are calculated for individual glass units, the system checks all four edges of the glass (top, left, bottom, right).

**If an edge is touching the sash** (stile, head, bottom rail) - the system calculates glass hidden in rebate as per actual size calculation for glass in sash section above.

**If an edge is touching a Georgian glazing bar** - this is calculated as follows:  
*GB Glazing Rebate Width = (GB Width - Tail) / 2*

**If the glazing tolerance around the four edges of the glass is the same** - This is calculated as follows:  
*Glass Hidden in Rebate = GB Glazing Rebate Width - Glazing Tolerance*

***Note:** This means, that the system may add different amount to the four sides of the glass depending on the Georgian glazing bar details.*

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