How the glass load calculation works
GlassLoad.com is an ASTM E1300 calculator for glass load resistance and glass thickness. It checks one rectangular lite of monolithic glass, simply supported on all four sides, on three sides with one free edge or on two opposite sides, or supported on one edge as a cantilever. It also checks laminated glass of two plies supported on four sides, on three sides, on two opposite sides or on one edge. It follows ASTM E1300 and gives you a load resistance, a deflection and a pass or fail against the design load.
What you enter
The long dimension a and the short dimension b, the nominal thickness, the glass type (annealed glass, heat strengthened glass or fully tempered glass), the load duration (short, 3 seconds, or long, 30 days), the design load and the E1300 edition. A thickness override is optional. Use US units (inches and psf) or SI units (millimeters and kPa). Results show both.
Step 1: the non factored load (NFL)
The NFL glass value is the load a lite of annealed glass can carry for a short duration load, for its size and thickness. E1300 prints it as a set of charts. GlassLoad.com calculates it for your exact size, so you do not read a chart by eye. The calculated NFL is checked against the printed E1300 charts. Where the chart gives no value, a plate analysis is used, and the result says so.
Step 2: glass type factors
The glass type factor (GTF) accounts for the glass type and the load duration. For a single lite and a short duration load it is 1.0 for annealed glass, 2.0 for heat strengthened glass and 4.0 for fully tempered glass. For a long duration load it is 0.43, 1.3 and 3.0.
Step 3: load resistance of glass
Load resistance (LR) is the NFL multiplied by the glass type factor. The check passes when the design load p, such as a wind load on glass or another window glass design load, is at most the load resistance. The report also shows the utilization p/LR as a decimal.
Step 4: center of glass deflection
The glass deflection calculator part uses the equation in E1300 Appendix X1 (Appendix X2 in E1300 09a). It is a curve fit to test data, so the deflection is approximate. It can differ from the true value by about 10 percent. Where deflection governs, verify it by an independent method.
The PDF report
The PDF report lists every input and every intermediate value in both unit systems. Plain warnings appear on screen and in the report whenever a result needs care.
Probability of breakage
For annealed glass the result also shows the probability of breakage at the design load. It is for information. Pass or fail follows the load resistance. It is not shown for heat strengthened or fully tempered glass.
Minimum glass thickness
The minimum thickness finder runs the check for every thickness offered by the edition and marks the thinnest glass that passes the design load. Use it to get a minimum glass thickness for a given size, glass type and load. It needs a free account.
The editions
GlassLoad.com covers E1300 09a, E1300 12a, E1300 16 and E1300 24. The edition sets the thicknesses offered, the largest design load within the scope of that edition and the name of the deflection appendix. The same E1300 calculator inputs work for all four.
Warnings, in plain words
The result carries a warning whenever one of these applies. The same text appears on screen and in the PDF report.
- The deflection is approximate and can differ from the true value by about 10 percent.
- The load is below one third of the load resistance, so the deflection is a rough value.
- The aspect ratio is above 5, so deflection is calculated as if it were 5 and the real deflection can be larger.
- The aspect ratio is above 10, or the size and thickness are outside the range calculated for this tool. Verify the load resistance by another method.
- For 25 mm glass, the printed chart gives a load about 6 percent lower than the value calculated from the minimum thickness. The report says which one was used.
- The design load is above the largest load within the scope of the edition. Verify the glass by another method.
- The deflection is larger than the glass thickness, so it is rounded as E1300 requires.
- The load is so low that the appendix does not apply, so no deflection is reported.
Your subscription and standards
Your subscription covers one standard with all its editions, chosen at sign up. To use another standard, request a switch on your Account page; it takes effect after 24 hours. Tokens for other standards are coming soon. Questions: support@glassload.com.
What is not covered yet
GlassLoad.com does not work out the wind load for your building. You enter the loads.
ASTM E1300
- Laminated glass of more than two plies.
- Non rectangular shapes.
- Glass guards and balustrades.
- Point supported glass.
- Thermal stress.
AS 1288:2021
- Human impact (Section 5), balustrades and barriers.
- Fins and point fixings.
- Sloped glazing.
- The wind pressure helper of the appendix.
- AS 1288:2006.
- Laminated glass with unequal sheets or an interlayer other than PVB.
EN 16612:2019
- National annexes. The recommended values of the standard are used.
- Cavity temperature from sunlight.
- Triple insulating units.
- Edge seal forces.
- Point fixings and fins.
- Non rectangular glass.
- A minimum thickness finder.
IS 16231:2019
- Human impact and safety glass selection (IS 16231 Part 4).
- Fire resistant glass.
- Seismic and imposed loads.
- Glass fins, structural glazing, frames and glazing details.
- Thermal stress.
- The wind pressure itself.
Use with care
GlassLoad.com is an independent tool. It is not affiliated with ASTM. The PDF report is a calculation record. Results are to be verified by a qualified professional.