Shellac Calculator works out the flake weight and alcohol volume needed for a pound cut. It also sizes a batch from surface area and coats, and thins a premixed can to a lower cut.
A pound cut is pounds of dry flakes per US gallon of alcohol. Pick what you know and the tool works out the rest.
Coverage and Film
Zinsser rates its Bulls Eye shellac and SealCoat at 400 to 600 sq ft per gallon (37 to 55 m² per gallon), less on porous wood. Use the low end for bare wood.
Prices
Enter what you paid. Metric prices are per kilogram and per liter.
Pound Cut Mixing Chart
| Cut | 1 Cup | 1 Pint | 1 Quart | 1 Gallon |
|---|---|---|---|---|
| 1 lb | 1 oz | 2 oz | 4 oz | 16 oz |
| 1.5 lb | 1.5 oz | 3 oz | 6 oz | 24 oz |
| 2 lb | 2 oz | 4 oz | 8 oz | 32 oz |
| 2.5 lb | 2.5 oz | 5 oz | 10 oz | 40 oz |
| 3 lb | 3 oz | 6 oz | 12 oz | 48 oz |
Ounces of flakes by weight per volume of alcohol, matching the shellac.net pound cut chart. The finished mix ends up about 10% larger per pound of cut.
Thinning Chart for Premixed Shellac
| Cut Change | Alcohol : Shellac | Easy Parts | Older Zinsser Label |
|---|---|---|---|
| 3 → 2.5 lb | 0.15 : 1 | 1 : 7 | Not listed |
| 3 → 2 lb | 0.38 : 1 | 2 : 5 | 2 : 5 |
| 3 → 1.5 lb | 0.77 : 1 | 3 : 4 | Not listed |
| 3 → 1 lb | 1.54 : 1 | 3 : 2 | 3 : 2 |
| 2 → 1.5 lb | 0.28 : 1 | 2 : 7 | Not listed |
| 2 → 1 lb | 0.83 : 1 | 4 : 5 | 1 : 1 |
| 2 → 0.5 lb | 2.50 : 1 | 5 : 2 | Not listed |
Exact values count the room dissolved flakes take up in the can. Zinsser's older label printed easy parts, and its current Bulls Eye sheet says not to thin. Zinsser's pre-stain conditioner mix of equal parts alcohol and SealCoat works out to about a 0.9 lb cut.
Shellac Calculator for Mixing Flakes and Thinning Cans
A pound cut is the number of pounds of dry shellac flakes dissolved in one US gallon of denatured alcohol. The Shellac Calculator turns that ratio into ounces of flakes and fluid ounces of alcohol for any batch size, from a pint for a picture frame to a gallon for a floor.
Woodworkers mixing a pint of 2 lb cut for a tabletop, restorers preparing a thin cut for French polishing, and finishers thinning a can of Zinsser shellac all start from the same conversion. It works from the alcohol you will pour, the finished volume you want, or the flakes on hand, and has separate modes for sizing a batch from surface area and for thinning a premixed can.
Pick a mode and enter one known amount
Choose a mode, enter the pound cut, then add the one amount you know. Units are US by default (ounces, fluid ounces, inches, square feet per gallon), with a metric switch. Surface sizes are finished dimensions, so a 1x6 board is entered as 3/4 by 5-1/2 inches, not by its nominal size.
Shellac Calculator math: from pound cut to flake weight
The pound cut is a trade convention rather than a formal standard, and Jeff Jewitt in Fine Woodworking documents it as pounds of shellac resin dissolved in a gallon of alcohol. A gallon holds 128 fluid ounces and a pound is 16 ounces, so each pound of cut works out to one ounce of flakes for every 8 fluid ounces of alcohol.
Here F is flake weight in ounces, C is the cut in pounds per gallon, and A is alcohol in US fluid ounces. Jewitt's own example fits, since 2 ounces of flakes in 8 ounces of alcohol makes a half pint of 2 lb cut. In metric, each pound of cut is 119.8 grams of flakes per liter of alcohol, so a 2 lb cut is about 240 grams per liter.
Weigh the flakes rather than scooping them, because a cup of crushed flakes holds far more shellac than a cup of whole flakes. Measuring by volume quietly shifts the cut without any sign that it happened.
Why the finished shellac is larger than the alcohol you pour
Dissolved flakes take up room, and Jewitt reports that 2 lb of shellac in a gallon of alcohol makes about 1.2 gallons, so a gallon of finished 2 lb cut holds only 1.66 lb of resin. His figures for 3 lb and 4 lb run to roughly 1.3 and 1.4 gallons, which is about 0.1 gallon, or 12.8 fluid ounces, per pound of flakes, and the calculator uses that value.
V is the finished volume and R is the pounds of resin in each gallon of finished shellac. Pour a full quart of alcohol for a 2 lb cut and the jar ends up holding about 38 fluid ounces, not 32, which is why the calculator asks whether you know the alcohol, the finished volume, or the flakes on hand.
Thinning a can of Bulls Eye or SealCoat to a lower cut
Clear and amber Bulls Eye are sold as a 3 lb cut and SealCoat as a 2 lb cut, and Bob Flexner in Popular Woodworking notes that the 3 lb can is too thick to brush without marks. Displacement changes the thinning arithmetic, because the alcohol already in the can is less than the can's volume.
Here x is the volume of alcohol to add per 1 part of shellac at the starting cut C1 to reach the target cut C2. Thinning 1 quart (32 fluid ounces) of 3 lb shellac to 2 lb gives x = 0.385, so add about 12.3 fluid ounces, close to 2 parts alcohol to 5 parts shellac. When the target is heavier than the can, alcohol cannot help, so the calculator returns flakes to dissolve in instead.
Equal parts rarely land where people expect. A 1:1 mix of 3 lb shellac and alcohol comes out near 1.3 lb, not 1.5 lb, and equal parts of SealCoat and alcohol come out near 0.9 lb, not 1 lb. Zinsser's SealCoat data sheet calls for that equal-parts mix as a pre-stain conditioner on soft woods such as pine, and the Wood Stain Calculator covers the stain that follows.
Zinsser's current Bulls Eye Shellac data sheet says not to thin that product, while its older bulletin printed reduction ratios of 2:5 for a 2 lb cut and 3:2 for a 1 lb cut, both close to the values above. Anyone who thins a 3 lb can anyway should test the cut on scrap wood first.
Shellac per coat from surface area and spread rate
Zinsser rates its Bulls Eye and SealCoat shellacs at 400 to 600 square feet per gallon in practical coverage, a manufacturer figure for canned shellac rather than a standard, and the calculator's spread-rate presets come from that range.
The range already assumes 15% material loss and shifts with surface porosity, so a large waste percentage stacked on top of it adds a second cushion.
V is finished shellac in fluid ounces, S is surface area in square feet (length times width times faces, divided by 144), Sr is the spread rate in square feet per gallon, N is the number of coats, and W is the waste fraction.
A 48 by 36 inch top with one face, three coats, a 2 lb cut, 400 square feet per gallon, and 10% waste needs about 12.7 fluid ounces of finished shellac, which splits into 10.6 fluid ounces of alcohol and 2.6 ounces of flakes.
One gallon is 231 cubic inches and one square foot is 144 square inches, so a gallon spread over a square foot is 1.604 inches, or 1,604 mils, thick. At 400 square feet per gallon that is a 4.0 mil wet film, and a 2 lb cut is 16.7% resin by volume, so each coat dries to about 0.67 mil.
Zinsser's sheet agrees, since 1,604 times the 19.3% solids by volume it lists for Bulls Eye Shellac gives the 310 square feet per gallon it prints as theoretical coverage at 1 mil.
Thinner cuts build slowly, since a 1 lb cut leaves about 0.37 mil per coat against 0.67 mil for a 2 lb cut at the same spread rate. That fits Flexner's point that thinning shellac to reduce ridging means more coats for the same film.
If a varnish or lacquer topcoat follows a dewaxed sealer coat, the Varnish Coverage Calculator and the Lacquer Calculator size that topcoat. The Sanding Schedule Calculator sets the grit sequence between coats, and the Finish Drying Time Calculator scales label cure times for the finish on top.
Input limits and where the math stops making sense
The calculator accepts pound cuts from 1/4 to 8 (30 to 960 grams per liter), alcohol from 0.5 to 2,560 fluid ounces, flake weight from 0.05 to 1,600 ounces, surface sides from 1 to 1,200 inches, spread rates from 50 to 2,000 square feet per gallon, and waste from 0 to 100%.
Coats run from 1 to 50 and faces from 1 to 1,000, both as whole numbers. Anything outside a range is flagged instead of calculated, and prices can be left blank.
Above a 3 lb cut the tool warns that the mix is stock strength, since heavier cuts are hard to brush evenly and standard mixing charts stop at 3 lb. Canned shellac does not match a freshly mixed cut exactly.
Zinsser lists Bulls Eye at 19.3% solids by volume and SealCoat at 15.5%, under the 23.1% and 16.7% that fresh 3 lb and 2 lb cuts work out to, so film estimates for cans run slightly high.
Drying and coverage vary with temperature, humidity, wood species, and ventilation, and alcohol vapor is flammable, so mix and brush where air moves and no flame or spark is near.
Entry slips that throw off a shellac batch
Reading a recipe as pounds per pint or quart is the costliest slip, since 1 lb of flakes in a pint is an 8 lb cut rather than a 1 lb cut. Mixing up the cut of a can skews any thinning result, because Bulls Eye clear and amber are 3 lb while SealCoat is 2 lb.
Using the top of Zinsser's 400 to 600 square feet per gallon range on bare, open-grain wood risks underestimating the shellac, since Zinsser ties the rate to surface porosity.
Shellac Mixing and Pound Cut Questions
How much shellac flakes do I need per pint of alcohol?
A pint (16 fluid ounces) takes 2 ounces of flakes for a 1 lb cut, 4 ounces for a 2 lb cut, and 6 ounces for a 3 lb cut. The finished pint runs about 10% over per pound of cut, so the 2 lb batch fills roughly 19 fluid ounces once the flakes dissolve.
Is shellac measured by weight or by volume?
Flakes are measured by weight and alcohol by volume, because a cut is pounds of flakes per gallon of alcohol. One ounce of flakes in one cup (8 fluid ounces) of alcohol is a 1 lb cut, and scooping the flakes by the cup is what throws that ratio off.
How do I thin Zinsser Bulls Eye shellac to a 2 lb cut?
Add about 0.4 parts alcohol per part of shellac, which is 12.3 fluid ounces per quart, a figure that counts the room the flakes take up. Zinsser's older label gave 2 parts alcohol to 5 parts shellac, though its current Bulls Eye data sheet says not to thin the product.
How long does mixed shellac last?
Jewitt puts the shelf life of user-mixed shellac at about six months to a year, and in his testing dewaxed solutions under six months old resisted moisture best. Flexner says dry flakes usually keep for years unless stored hot or bleached, and Zinsser lists three years for a sealed can.
Can I use Everclear or isopropyl alcohol instead of denatured alcohol?
Woodworkers use denatured alcohol, 190-proof grain alcohol, or 90 to 99% isopropyl, and the advice is to pick the purest, lowest-water option available. Jewitt describes typical denatured alcohol as 190-proof ethanol with 4% methanol and 1% MIBK, and finds that 200-proof ethanol dissolves flakes slightly faster without improving durability.
What is a 2 lb cut of shellac in grams per liter?
One pound of flakes per US gallon is 119.8 g/L, so a 2 lb cut is about 240 g per liter, or 24 g per 100 mL of alcohol. Pound cuts assume the 3.785 liter US gallon, and the 4.546 liter imperial gallon gives only 99.8 g/L for a 1 lb cut, which is about 17% thinner.