Floor Insulation Calculator
Insulating a floor over an unheated space is the fastest fix for cold feet. Enter the footprint and joist layout for bay counts and batt quantities.
Your project
Covers cuts, compression and odd bays. 10% is the usual default.
Your results
- Floor area
- 720 sq ft
- Joist bays
- 18 bays
- Each about 30 ft long
- 8 ft batts required
- 82 pieces
- R-value achieved
- R-29.6
- Recommended for your zone
- R-30
- R-0.4 short
- Support rods needed
- 246 rods
- About one every 16 in along each bay
- Material cost
- $952
Estimates use typical US material and labor pricing. Confirm quantities against the coverage chart on the bag before you buy.
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Gear for this job
Fiberglass Batt Insulation R19
Insulation Support Rods
U0U 16 Inch Insulation Support Wire,30 Pcs Insulation Hangers Bracket Metal Support Rods,Stainless Steel Metal Insulated Wire for Attic,Garage,Ceiling Insulation (30, 16inch)
$11.99
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ELECFUN 2 Inch P Clamps Rubber Cable Holders R Clips Cord Wire Hangers
$9.99
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uxcell Foam Tubing for Handle Grip Support, Pipe Insulation, 25mm(1") ID 35mm OD 1m Length Black
$12.59
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Staple Gun Insulation
Arrow 508 Heavy Duty T50 1/2-Inch Leg Length, 3/8-Inch Crown, Staples for Upholstery, Construction, Furniture, Crafts, 1250 Count(Pack of 1)
$3.97
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Upholstery Staple Gun Heavy Duty, YEAHOME 4-in-1 Stapler Gun with 4000 Staples, Manual Brad Nailer Power Adjustment Stapler Gun for Wood, Crafts, Carpentry, Decoration DIY
$16.99
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meite T50 Staples, 3/8 Inch Staples for Staple Gun, Heavy Duty Galvanized Staples, 20 Gauge 3/8" Crown, Compatible with T50 Staple Gun, Ideal for Upholstery, Construction, Furniture (1,512 Counts)
$6.98
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Prices as of Oct 11, 2026, 4:41 AM UTC. Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
How this calculator works
- Floor area = length × width
- Bays = width in inches ÷ joist spacing
- Batts = area × (1 + waste %) ÷ area per batt
Keep going
- Floor batts cut noise between levels; for echo inside a room, use the reverberation time (RT60) calculator
- The usual floor batt: R-19 insulation calculator
Frequently asked questions
Which way does the paper facing go on floor insulation?
Facing toward the heated side — that means up, against the subfloor. In humid southern climates unfaced batts are often the better choice.
How do I hold floor batts up?
Wire support rods (lightning rods) every 16 inches, or house wrap stapled across the joists. Never rely on friction — batts sag and lose their R-value once there's a gap.
Which way should floor insulation face?
Any vapour retarder faces the heated side, so in a floor over an unheated crawlspace or garage the facing goes up, toward the room. Getting it upside down puts the retarder on the cold side, where moisture moving up from below can condense against it inside the assembly.
How do I stop floor batts from falling down?
Support them mechanically rather than by friction. Wire insulation supports sprung between the joists every couple of feet are the usual method; netting or lath also works. Batts that rely on friction alone will sag within a few seasons, and a sagging batt with an air gap above it is doing very little.
Will insulating the floor make it warmer underfoot?
It will stop the floor pulling heat out of the room, which is what most people are actually feeling. It will not make the floor warm the way radiant heating does. If the complaint is specifically cold feet on tile, insulation helps but underfloor heating is the thing that solves it.
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Floor area
720 sq ft