Wood Filler Calculator

Wood Filler Calculator for nail holes, cracks, gouges and dents. It works out the filler volume each repair holds, the container to buy, how many layers to build, and when to sand.

Sizing a Repair With the Wood Filler Calculator

The Wood Filler Calculator works out how much filler a set of holes, cracks, gouges or dents will actually hold. It then turns that volume into the container to buy, the layers to build and the wait before you can sand.

Trim carpenters use it to size a tube for a room of nail holes. Furniture restorers use it for deeper gouges, where the layer limit on the label decides how long a repair takes far more than the amount of filler does.

Measuring the Hole, Crack or Dent

Pick the shape that matches the damage, then enter the count and its size in inches or millimeters. Gouges and cracks take length, width and depth, while nail holes and dents take a diameter and a depth.

Measure after you clean out loose fibers and old filler, since the empty space is what the filler has to take up. Depth runs from the finished surface to the bottom of the void, and a crack is measured at its widest point.

A job with two kinds of damage, such as a door with twenty nail holes and one long split, goes in the Second Defect Type panel. Both are added together before the extra allowance, so one container covers the whole repair.

The Volume Math for Each Defect Shape

Each shape holds a different share of its outside size. A square-sided gouge is a simple box, and a V-shaped crack narrows to nothing at the bottom, so it holds half as much.

$$V_{gouge}=L\times W\times D{V}_{crack}=\frac{L\times W\times D}{2}$$

A nail or screw hole is a cylinder, which holds about 79 percent of a square hole of the same size across. A bowl-shaped dent is a spherical cap, where d is the diameter across the rim and h is the depth at the center.

$$V_{hole}=\frac{\pi d^{2}D}{4}{V}_{dent}=\frac{\pi h}{6}\left(\frac{3d^2}{4}+h^2\right)$$

The dent formula only works when the depth is no more than half the diameter, since a deeper bowl stops being a cap. The calculator flags that entry and points you to Nail or Screw Hole for a deep round void.

The total is every defect's volume times its count, plus the extra you set for overfill and sanding. That extra covers the mound left proud of the surface, the dust sanded off and the paste left on the knife.

$$V_{buy}=\left(\sum q\times V\right)\times \left(1+\frac{x}{100}\right)$$

Three gouges 4 in long, 1/2 in wide and 3/8 in deep hold 0.75 cu in each, or 2.25 cu in together. With the default 20 percent extra that comes to 2.7 cu in, which is about 1.5 fl oz of filler.

Counts must be whole numbers from 1 to 100,000, and the extra can run from 0 to 300 percent. Lengths and diameters stop at 240 in, widths at 48 in and depths at 24 in, and any entry outside those limits pauses the results and highlights the field.

Nail Holes Barely Use Any Filler

A 1/8 in nail hole set 1/8 in deep holds about 0.0015 cu in, or roughly 0.025 mL. A hundred of them take about 2.5 mL, which is less than a teaspoon of filler.

At that scale, what sticks to the putty knife and what gets sanded off the overfill far outweighs the holes. The calculator switches to a note when each hole holds under 0.05 mL, suggesting 50 percent extra or more and the smallest tube on the shelf.

Why Label Ounces Mislead on Paste Filler

Paste fillers are sold by net weight, so the ounces on the label are not fluid ounces. How much filler is inside depends on how heavy the paste is compared with water.

$$V_{floz}=\frac{W_{oz}\times 28.35}{SG\times 29.57}$$

W is the net weight on the label, SG is specific gravity, 28.35 converts ounces to grams and 29.57 converts milliliters to fluid ounces. The container table in the Wood Filler Calculator runs every size for the filler you picked through this step.

A dense latex paste at a specific gravity of 1.7 holds only about 0.56 fl oz for every ounce on its label. A 6 oz tub of it holds about 3.4 fl oz, so a heavy filler runs out well before its label suggests.

For a filler not in the list, pick Other Filler and enter the label size, whether the label is by weight or volume, and the density. Specific gravity is usually printed on the maker's safety data sheet.

Layer Limits and Dry Times From the Makers

Most one-part fillers dry by losing water or solvent, so thick passes shrink and crack. The calculator splits the deepest defect into layers no thicker than the maker allows, then multiplies the dry time per layer.

Minwax says not to use Stainable Wood Filler on holes larger than 3/4 in and points to its two-part High Performance filler for those. It also asks you to fill slightly above the surface so there is something to sand flush.

DAP's Plastic Wood-X data sheet shows how fast dry time climbs with depth. A 1/8 in fill is ready in 2 to 6 hours, while a 1/4 in fill needs about 36 hours, so a 1/2 in gouge built in two layers takes three days before sanding.

Two-part products change the plan. 3M lists Bondo Wood Filler as workable for only 3 to 4 minutes once mixed, so mix small batches. WoodEpox is a 1:1 epoxy putty that the CAMEO conservation database describes as usable in any thickness, which is why the tool treats it as one pour.

When Filler Is the Wrong Fix

On the Minwax blog, its writer suggests gluing in real wood, such as a dowel, for holes larger and deeper than 1/4 in. A wood plug takes stain like the board around it, which no paste filler fully does.

DAP also says that if the wood is to be stained, stain it before filling. Filling first seals the pores around the hole, and the halo shows up once the stain goes on.

Minwax lists its Stainable Wood Filler as not recommended for floors. Floor repairs need a different product, and the sanding around any patch is sized in the Sanding Schedule Calculator.

Wood Filler Questions From the Shop

Why doesn't stainable wood filler take stain like the wood?

Filler has no wood pores, so it soaks up stain differently. On a Fine Woodworking forum thread, finishers point out that the wood also changes color as it ages while the filler does not, so even a good match drifts.

The fixes they describe are picking a filler close to the final stained color, or touching up the patch with artist's oil paint after staining. Test on scrap with filler, stain and topcoat before you commit, and size the stain itself with the Wood Stain Calculator.

Does wood filler shrink as it dries?

Water-based and solvent fillers lose volume as the liquid leaves, which is why makers ask for a slight mound over the hole. On a WoodWeb furniture forum, one maker notes that water-based Famowood tints and sands well but shrinks more than solvent-based fillers.

Two-part fillers cure by chemical reaction instead. 3M describes Bondo Wood Filler as non-shrinking, and WoodEpox is sold as a shrink-free epoxy, so both can fill deep voids in fewer passes.

Is one small tube enough for a room of nail holes?

Almost always, because each small hole holds only a fraction of a milliliter. What runs a tube out is the overfill that gets sanded away and the paste left on the knife, not the holes themselves.

For paint-grade trim the choice of filler matters less than the prep. Sand it flush before priming, and size the paint for the room in the Paint Coverage Calculator.