Added insulation, target R and thickness in inches
Calculate the resistance added by a homogeneous insulation layer, the gap to your supplied target and the thickness needed. Enter US R-values and a product-specific R per inch; the result also shows millimetres and cubic metres.
Calculator: illustrative inputs — Added layer
Calculator: illustrative inputs — Thickness in inches
Calculator: illustrative inputs — k to R
Added layer and existing resistance
Radded,US = thickness [in] × RUS per inch; Rtotal,US = Rexisting,US + Radded,US
Illustrative inputs: existing US R-19 plus 6 inches at US R-4 per inch gives R-43. A separately established R-49 target still has a gap of R-6. The target is supplied by you, not inferred from a climate or application preset. Resistances may be added only for compatible homogeneous layers in series. Framing, gaps and moisture can change effective assembly performance.
Attics, floors and a justified target
drequired [in] = max(0, Rtarget,US − Rexisting,US) / RUS per inch
With R-19, target R-49 and R-4 per inch, the required added thickness is 7.5 inches (190.5 mm). Over 100 ft² this geometrically contains about 0.177 m³. This volume is not a loose-fill bag count: use installed density, settling and coverage data from the exact product. Identify whether insulation belongs at the attic floor, roof slope or suspended floor, and establish the local requirement separately.
Thickness from US k-value
d [in] = RUS × k [Btu·in/(h·ft²·°F)]
For illustrative R-19 and k = 0.25, thickness is 4.75 inches or 120.65 mm. This k-value uses an inch in its numerator; conductivity expressed per foot has a different numerical value. Do not insert SI lambda directly into this form. One inch is exactly 25.4 mm.
k-value versus layer R
RUS = d [in] / k; RSI = RUS / 5.678263341
At 6 inches and k = 0.25, layer resistance is US R-24, about RSI 4.227 m²·K/W. R includes thickness; k and lambda describe conductivity. Compare complete assemblies in the same units, with the same surface terms and conditions. A stock thickness must be checked against the product documentation before purchase.