Arithmetic example: 1,000 ft² at an entered 36.5-bag rate
A 40 × 25 ft area is 1,000 ft². With an illustrative entered rate of 36.5 bags per 1,000 ft² and no extra, the calculation is 1,000 ÷ 1,000 × 36.5 = 36.5, rounded up to 37 bags. This is the calculator’s example rate, not a recommendation for your product or thermal target.
Match the chart to the material in the bag
Record the product name, bag mass, chart revision and installation method before entering a rate. A loose-fill attic row is not interchangeable with a dense-pack wall row. Choosing a different thermal target also changes the chart rate. Greenfiber publishes product-specific coverage documents; use the current document supplied for the exact product you will install.
Do not convert a desired R-value into bags by dividing by a generic R-value per inch. The calculator accepts a chart quantity after that product decision has been made. It does not choose the thermal requirement for your building or determine whether an existing layer can remain.
Measure the area receiving this same treatment
Sketch the footprint and divide irregular areas into rectangles. Deduct only areas excluded from the specified treatment, and record why each deduction was made. Keep an inaccessible bay visible as a separate question rather than silently removing it from the estimate. Different depths or products need separate lines.
The chart-rate field remains bags per 1,000 ft² even when your measurements are metric. The engine converts area for you. For reference, 1,000 ft² equals 92.90304 m². Do not enter a bags-per-square-metre rate into that field without converting its basis.
Keep settlement and extra material separate
Manufacturer charts can specify both minimum bag quantity and installation thickness. Reaching one does not automatically prove that the other has been achieved. Record both requirements from the same chart and compare them with the installer’s completion record.
Optional extra begins at zero because chart assumptions may already address settlement. Add a separate allowance only when you can explain the additional loss or scope it covers. A second automatic settlement percentage can inflate an order while hiding what the product chart actually required.
Check the order before delivery
Ask the installer which equipment and application method will be used, and make sure the quoted bags match the chart. Retain the label or chart with the estimate so a substituted product triggers a recalculation. A cheaper price per bag is not necessarily cheaper coverage when bag mass and chart rates differ.
Keep access preparation, ventilation details and any remedial work outside this material count. Those items need their own scope and qualified assessment; extra bags cannot compensate for a different installation system.
Do it in order
- Identify the exact chart and application row.
- Measure the area in a single unit system.
- Enter its minimum bags per 1,000 ft².
- Document any extra allowance, then round up once.
Planning boundary
This is a product-chart quantity calculation, not a thermal design or an installation acceptance certificate.
Sources checked
Can I order only by depth?
Keep both the chart’s minimum bags and depth requirements. A depth observation alone does not identify the installed material quantity.
Does changing to metric change the chart rate?
No. The labeled chart rate stays per 1,000 ft²; the calculator converts the measured area internally.