How to Calculate Resin Volume for Any Shape
Every epoxy project is just a volume problem. Once you know the shape's volume in cubic inches (or cm³ for metric), one simple division gives you the fluid ounces of resin needed. This guide covers every common shape with formulas, worked examples, and pre-calculated tables.
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Once you have the volume in cubic inches, converting to fluid ounces is one step:
Gallons = Fluid ounces ÷ 128
Metric: mL = cm³ (direct — no conversion needed)
Litres = cm³ ÷ 1000
The constant 1.805 comes from the fact that 1 US fluid ounce of liquid = 1.80469 cubic inches. For metric, volume in cm³ equals volume in mL, making the math straightforward.
Volume Formulas by Shape
Rectangular / Box Mold
Example: A 6×4×2 inch resin tray mold:
6 × 4 × 2 = 48 cu in ÷ 1.805 = 26.6 fl oz → add 10% = 29.3 fl oz
| Length | Width | Depth | Cu In | Fl Oz (+ 10%) |
|---|---|---|---|---|
| 3 in | 3 in | 1 in | 9 | 5.5 fl oz |
| 4 in | 4 in | 1 in | 16 | 9.8 fl oz |
| 6 in | 4 in | 1 in | 24 | 14.6 fl oz |
| 6 in | 4 in | 2 in | 48 | 29.3 fl oz |
| 12 in | 6 in | 1 in | 72 | 43.9 fl oz |
| 12 in | 9 in | 2 in | 216 | 131.7 fl oz |
Cylinder Mold
(π ≈ 3.14159, radius = diameter ÷ 2)
Example: A cylinder mold 3 inches diameter × 4 inches tall:
3.14159 × 1.5² × 4 = 28.27 cu in ÷ 1.805 = 15.7 fl oz → add 10% = 17.2 fl oz
| Diameter | Height | Cu In | Fl Oz (+ 10%) |
|---|---|---|---|
| 2 in | 2 in | 6.3 | 3.8 fl oz |
| 3 in | 3 in | 21.2 | 12.9 fl oz |
| 4 in | 4 in | 50.3 | 30.7 fl oz |
| 6 in | 6 in | 169.6 | 103.4 fl oz |
Sphere Mold
Example: A 4-inch diameter sphere mold (radius = 2 in):
(4/3) × 3.14159 × 2³ = 33.51 cu in ÷ 1.805 = 18.6 fl oz → add 10% = 20.4 fl oz
| Diameter | Cu In | Fl Oz (+ 10%) |
|---|---|---|
| 1 in | 0.52 | 0.3 fl oz |
| 2 in | 4.19 | 2.6 fl oz |
| 3 in | 14.1 | 8.6 fl oz |
| 4 in | 33.5 | 20.4 fl oz |
| 6 in | 113.1 | 69.0 fl oz |
Hemisphere / Dome Mold
Half the volume of a full sphere. A 4-inch dome mold = 33.51 ÷ 2 = 16.75 cu in ÷ 1.805 = 9.3 fl oz (+ 10% = 10.2 fl oz).
Cone Mold
Example: A cone mold 4 in base diameter × 5 in tall:
(1/3) × 3.14159 × 2² × 5 = 20.94 cu in ÷ 1.805 = 11.6 fl oz
Irregular shapes tip: Fill the mold with water, pour it into a measuring cup. Read mL from the cup — that number of mL equals the same number of grams of water and approximately the same volume in mL of resin. Convert mL to fl oz by dividing by 29.57.
Quick Conversion Reference
| From | To | Multiply by |
|---|---|---|
| Cubic inches | Fluid ounces | ÷ 1.805 |
| Fluid ounces | Cubic inches | × 1.805 |
| Fluid ounces | US gallons | ÷ 128 |
| cm³ (mL) | Fluid ounces | ÷ 29.57 |
| Litres | Fluid ounces | × 33.81 |
| Litres | US gallons | × 0.2642 |
Frequently Asked Questions
How do I convert cubic inches to fluid ounces for epoxy?
Divide cubic inches by 1.805 to get fluid ounces. This constant reflects that 1 US fluid ounce of liquid = 1.80469 cubic inches. For example: a 4×4×2 inch mold = 32 cu in ÷ 1.805 = 17.7 fluid ounces of epoxy resin. Add 10% for losses = 19.5 fl oz.
How do I calculate resin for a cylinder mold?
Use π × radius² × height to get cubic inches, then divide by 1.805. For a 3-inch diameter, 4-inch tall cylinder: radius = 1.5, volume = 3.14159 × 1.5² × 4 = 28.27 cu in ÷ 1.805 = 15.7 fl oz. Add 10% = 17.2 fl oz total.
How do I calculate resin for an irregular shape?
Use the water displacement method: fill the mold with water, pour that water into a measuring cup. The mL reading equals the volume in mL of resin needed. Divide by 29.57 to convert to fluid ounces. Add 10% for mixing and pouring losses.