Weight and hardware

Two calculators: what the framed picture weighs, built up from the published glass figures and a stated allowance for the rest; and what one named anchor is rated for in the wall you have.

Weight first, then the wall, then the hardware. That order is the whole of Hanging it, and these two boxes are the arithmetic in it. Write both results in the hanging plan, with the conditions the rating assumes.

1. What the framed picture weighs

Glass is usually most of the mass, and it is the one well published figure. Everything else is an allowance this manual computes and labels.

Assumptions

• Glass weight comes from a trade association's published table, reissued as current national association data: 1.2 pounds per square foot at 2.5 mm, 1.6 at 3 mm, 2.0 at 4 mm, 2.4 at 5 mm and 3.0 at 6 mm, with a density of 158 pounds per cubic foot for any thickness not on the table. See the flat glass weight table. Product-specific
• Acrylic is computed, not published: no maker publishes a weight-per-thickness table, so the box works from the specific gravity of 1.19 that two makers publish independently under two different test methods, one under ASTM D792 and one under ISO 1183. That figure is also the basis of the maker's own claim that acrylic sheet is half the weight of glass. Physical principle
• The frame allowance is ours. Nobody publishes moulding weight per linear foot. The box takes the section you type (face width by depth), runs it around the outside perimeter, and applies 0.55 grams per cubic centimeter for wood, 0.90 for composite, and aluminum at 2.70 taken as a quarter solid for a metal section. Every one of those densities is our assumption.
• The board allowance is ours: 0.26 pounds per square foot per board, from a board density of 0.8 grams per cubic centimeter at a sixteenth of an inch thick.
• Not included: the hanging hardware itself, a sealed package's extra layers, a float mount's spacers, glass with a coating, or an ornate frame's applied decoration. A kitchen scale under the finished piece beats every figure here, and takes a minute.
• The two-person line uses the load constant a national institute sets for lifting: 23 kilograms, about 51 pounds, described as safe under ideal conditions for 75 percent of females and 90 percent of males, and reduced by six multipliers for distance, height, twist, frequency and grip. A wide frame held away from the body is not ideal conditions. See the lifting equation summary. Convention

2. What one anchor is rated for

Choose a product and a wall and the box prints the maker's own ultimate test figure, a quarter of it as the working load, and the conditions that number assumes. Walls and hardware is the same data as a table you can filter.

Assumptions

• Every figure is the maker's own published ultimate test value, from its technical sheets rather than its product pages: the SNAPTOGGLE technical bulletin, the SnapSkru metric bulletin, the hollow-wall anchor bulletin, the ALLIGATOR catalogue page and the masonry screw technical notes. Product-specific
• The quarter is the makers' own. The toggle maker's published questions page states that industry safety standards recommend a quarter of the ultimate load as a reasonably safe working load, and says it cannot guarantee even that because it does not know the condition of your wall. The masonry screw sheet puts it as safe working loads not exceeding 25 percent of the ultimate capacity. Convention
• The same maker makes the point the rest of the trade leaves out: the ultimate value is for objects held close to the wall, and moving the load away from the wall greatly reduces what the anchor allows. A picture hangs close; a swing-arm mount does not.
• The gap between a technical sheet and a package is real and worth seeing. The maker's product page for the same anchor says it supports up to 238 pounds in 1/2 inch drywall, which is the ultimate figure with no safety factor mentioned anywhere on the page. The bulletin is the number to use.
• The margin rule is a practitioner guide's, prepared with a museum packing and handling network: hanging hardware should support 25 to 50 percent more than the artwork's maximum weight, and all methods should be re-checked annually. Convention
• Frame-side hardware is not in this box, because no tested rating for a D-ring, a screw eye or a strap hanger could be found. The ratings that exist sit on retail listings, disagree with each other for what looks like the same part, and state no test basis; one of them says in print that the rating assumes the hanger is nailed into a stud and is for comparative purposes only. Hardware by published rating covers it honestly. Ask the authority