Find the correct counterweight for your double-hung or single-hung window sash so it raises and holds smoothly.
7 Tips for Installing Proper Window Counterweights
Tip 1: Counterweights Exist to Balance Your Sash, Not to Lift It
Window counterweights don’t do the lifting work—they simply balance the weight of the glass and frame so your sash moves freely and holds position without jamming or dropping. A properly balanced window feels effortless to open and stays exactly where you leave it. Counterweights work on the principle that equal weight on both sides of a pulley creates equilibrium, which is why they must match the sash weight precisely.
Tip 2: Cast Iron Counterweights Are the Standard for Residential Windows
Cast iron is the traditional choice for window counterweights because it’s durable, holds its weight accurately over decades, and resists corrosion inside the window frame. Cast iron counterweights come in standard sizes, stacking one on top of another inside the frame pocket. Older windows sometimes used lead weights, but cast iron is safer and equally effective.
Tip 3: Your Sash Weight Determines the Counterweight Size You Need
The total weight of the glazed sash (glass, wood or frame material, and any hardware) is the starting point for calculation. A small single-hung window sash might weigh 8-15 pounds, while a large double-hung sash can weigh 35-40 pounds. You need one counterweight per sash, and each counterweight must equal the sash weight—so if your lower sash weighs 20 pounds, you need a 20-pound counterweight on each side of the frame.
Tip 4: Measure Your Sash Weight Accurately Before Ordering Counterweights
Remove the sash from the frame and weigh it on a bathroom scale—this single step prevents ordering the wrong size. If you cannot remove the sash, you can estimate using the glass area: multiply the width and height in square feet by 2.5 pounds per square foot for single-glazing, or 3.5-4 pounds per square foot for double-glazing, then add 2-4 pounds for the wood frame itself. Write down the exact sash weight immediately so you don’t forget mid-project.
Tip 5: Account for Both Upper and Lower Sashes Separately
If you have a double-hung window with both an upper and lower sash, weigh each one individually—they often differ in weight. Each sash needs its own matching counterweight on both sides of the frame. Older windows that have been reglazed with heavier modern glass will need heavier counterweights than the original installation, even if the window frame itself hasn’t changed.
Tip 6: Counterweight Pockets Must Be Deep Enough for the Weight Stack
Counterweights sit in vertical pockets inside the frame sides and move up and down as the sash moves. The pocket depth limits how many weights you can stack. Check your frame pocket depth before ordering—standard residential windows accommodate 12-18 inches of weight. If your sash is unusually heavy, you may need to use fewer, heavier weights rather than stacking many small ones.
Tip 7: Test Your Window After Installation to Confirm Proper Balance
After installing counterweights, open and close the window several times through its full range. It should move smoothly without sticking, stay in place when stopped at any height, and not slam shut or jump open. If the window feels unbalanced—either too heavy or too light—the counterweights may be slightly off or the sash cord may be catching. Minor adjustments in cord placement often fix this without replacing weights.
Where to Go From Here
Now that you understand sash weight, counterweight sizing, pocket depth, and balance testing, use our Window Counterweight Calculator to determine the exact weight you need for your window. Enter your sash weight and the calculator will tell you the counterweight size required for smooth, lasting operation.
Frequently Asked Questions About Window Counterweights
How do I know if my window counterweights are the wrong size?
If your window is hard to open, sticks partway through its travel, or suddenly slams shut or jumps open, the counterweights are likely mismatched. Too-light counterweights make the window feel heavy and make it drop suddenly when released. Too-heavy counterweights make it hard to push down and cause the sash to snap upward. Proper counterweights should make the sash feel nearly weightless—you can open or close it with one hand using just two fingers.
Can I replace counterweights without removing the window from the frame?
Yes—you can access counterweights through the pocket access doors on the sides of the frame without removing the sash if those access ports exist in your window design. If your window doesn’t have removable pocket covers, you’ll need to remove the sash and pull it partway out to reach the old weights and install new ones. Either way, the sash cord must be disconnected from the weight first.
What if I can’t find the exact counterweight size I need?
Standard cast iron counterweights come in 1-pound increments from 4 to 50 pounds. If your sash weighs 14 pounds but only 12-pound and 15-pound weights are available, err slightly under rather than over—cord and pulley friction takes up the difference, and a slightly-light counterweight is easier to adjust than removing one that’s too heavy. You can also stack multiple smaller weights in the pocket to reach your exact target weight.
How long do counterweights last?
Cast iron counterweights are virtually permanent indoors. They do not wear out, rust (when inside the frame), or lose weight over time. Original counterweights from 100-year-old windows still function perfectly. The only reason to replace them is if they were the wrong size to begin with, or if you reglaze your window with heavier modern glass.
Can I use different weight on each side of the window?
No—both sides must be identical in weight. Window sashes ride on the same cord-and-pulley system on both sides, so mismatched weights will cause the sash to bind, stick, or travel at an angle. Both counterweights pull up with equal force, which is what keeps the sash balanced and centered in the frame.