Calculate the PG and VG volumes, weights, and final ratio for any base mix, from a target PG/VG ratio, from two liquids blended together, or from what is already in the bottle.
PG VG Ratio Formula
The PG/VG ratio is a volume percentage split of a two component base: propylene glycol (PG) and vegetable glycerin (VG). Every mode below works from the same idea, that the PG volume divided by the total volume defines the ratio.
Component volumes from a target ratio
- V_PG = volume of propylene glycol to measure (mL)
- V_VG = volume of vegetable glycerin to measure (mL)
- V_T = total finished volume of the mix (mL)
- P = target PG percentage of the finished mix (%)
Ratio from volumes you already have
- P = PG percentage of the mix (%)
- V_PG, V_VG = measured volumes of each component (mL)
Final ratio after blending two liquids
- P_F = PG percentage of the finished blend (%)
- V_A, V_B = volumes of liquid A and liquid B (mL)
- P_A, P_B = PG percentages of liquid A and liquid B (%)
Correcting an existing mix to a target ratio
- V_VGadd = vegetable glycerin to add when the target PG is lower than the current PG (mL)
- V_PGadd = propylene glycol to add when the target PG is higher than the current PG (mL)
- V_C = current volume in the bottle (mL)
- V_PG = propylene glycol already in the bottle (mL)
- P_T = target PG percentage (%)
Batch weight from the volumes
- W = total weight of the base (g)
- 1.036 = density of propylene glycol at 20 C (g/mL)
- 1.261 = density of vegetable glycerin at 20 C (g/mL)
The four calculator modes map directly onto these expressions. The target ratio mode solves the first pair for V_PG and V_VG, and it subtracts flavor concentrate from whichever component carries the flavor so the finished bottle still lands on the ratio you asked for. The volumes mode solves for P so you can label a bottle you mixed by eye. The blend mode is a volume weighted average of two PG percentages, which is what happens whenever a second liquid is poured into a base. The correction mode inverts that average for the case where only one component is added, so the total volume rises as the ratio moves. The weight formula converts any of those results into grams, which is the form you need if you mix on a scale.
Common PG/VG Ratios, Weights, and Estimated Viscosity
PG and VG have very different densities and viscosities, so two bases with the same volume are not the same weight and do not flow the same way. The table below gives the measured volumes for a 30 mL batch, the weight of that batch, the mixture density, and an estimated blend viscosity at 20 C. Viscosities are estimated with a log linear blending rule using 56 cP for PG and 1,412 cP for VG, so treat them as approximate rather than measured.
| PG/VG | VG/PG | PG in 30 mL | VG in 30 mL | Mix density (g/mL) | Weight of 30 mL | Est. viscosity (cP) |
|---|---|---|---|---|---|---|
| 100/0 | 0/100 | 30.0 mL | 0.0 mL | 1.036 | 31.1 g | 56 |
| 60/40 | 40/60 | 18.0 mL | 12.0 mL | 1.126 | 33.8 g | 203 |
| 50/50 | 50/50 | 15.0 mL | 15.0 mL | 1.149 | 34.5 g | 281 |
| 40/60 | 60/40 | 12.0 mL | 18.0 mL | 1.171 | 35.1 g | 388 |
| 30/70 | 70/30 | 9.0 mL | 21.0 mL | 1.194 | 35.8 g | 536 |
| 20/80 | 80/20 | 6.0 mL | 24.0 mL | 1.216 | 36.5 g | 740 |
| 0/100 | 100/0 | 0.0 mL | 30.0 mL | 1.261 | 37.8 g | 1412 |
The second table shows how far the ratio moves when 10 mL of a second liquid is added to a 50 mL base. This is the arithmetic behind every complaint that a mix came out thinner than the label on the base bottle suggested.
| 50 mL base (PG/VG) | Final ratio with 10 mL of 100% PG | Final ratio with 10 mL of 50/50 | Final ratio with 10 mL of 100% VG |
|---|---|---|---|
| 20/80 | 33/67 | 25/75 | 17/83 |
| 30/70 | 42/58 | 33/67 | 25/75 |
| 40/60 | 50/50 | 42/58 | 33/67 |
| 50/50 | 58/42 | 50/50 | 42/58 |
Example Problems
Example 1: a 60 mL batch at 30% PG with flavoring
You want 60 mL of finished liquid at a 30/70 PG/VG ratio, and 10% of the bottle will be a PG based flavor concentrate.
- Flavor volume: 60 * 0.10 = 6 mL.
- Total PG the finished mix needs: 60 * 0.30 = 18 mL.
- The flavor is PG based, so it already supplies 6 mL of that. PG to measure: 18 – 6 = 12 mL.
- VG to measure: 60 * 0.70 = 42 mL.
- Check: 12 + 42 + 6 = 60 mL, and the PG share is (12 + 6) / 60 = 30%.
- By weight: 12 * 1.036 = 12.43 g PG, 42 * 1.261 = 52.96 g VG, plus about 6 g of concentrate, for roughly 71.4 g total.
If you had ignored the flavor carrier and measured 18 mL of PG, the finished bottle would sit at 40% PG instead of 30%.
Example 2: correcting a mix that is too high in PG
You have 30 mL of base at 50% PG and you want it at 30% PG without discarding anything.
- PG already in the bottle: 30 * 0.50 = 15 mL.
- That 15 mL has to become 30% of the new total, so the new total is 15 / 0.30 = 50 mL.
- VG to add: 50 – 30 = 20 mL.
- Check: PG is 15 mL, VG is 15 + 20 = 35 mL, and 15 / 50 = 30% PG.
Note that the fix costs volume. You cannot lower the PG percentage without making more liquid, so plan the ratio before you mix if bottle size matters.
FAQ
Is a ratio like 70/30 written PG first or VG first?
By convention in e-liquid labeling the VG number is written first, so 70/30 normally means 70% VG and 30% PG. The convention is not universal, and chemistry style writing usually puts PG first. The safest reading is the one where the larger number matches the thicker, sweeter component, which is VG. The calculator asks for a PG percentage explicitly and then reports the result in both notations so there is no ambiguity about which number is which.
Why do the gram amounts not match the milliliter amounts?
PG has a density of about 1.036 g/mL and VG about 1.261 g/mL at 20 C, a difference of roughly 22%. A 50/50 mix by volume is therefore about 45.1% PG and 54.9% VG by weight. If you mix on a scale using the volume numbers as if they were grams, a nominal 50/50 comes out closer to 55/45 in favor of PG. Weighing is more repeatable than syringes for large batches because it avoids the residue that thick VG leaves in a syringe barrel, but you have to convert first. The calculator prints both the volume and the weight for each component so you can pour or weigh from the same result.
Do the two volumes add up exactly?
Not quite. PG and VG are both hydrogen bonding liquids and blends of them contract very slightly, so 50 mL plus 50 mL yields marginally less than 100 mL. The excess volume of mixing for these two is well under 1% across the usual ratios, which is smaller than the error in a hand filled syringe, so the calculator treats volumes as additive. If you need exact final volume for a container, mix a little short and top up. Separately, if any liquid you are blending contains nicotine, be aware that nicotine is acutely toxic by skin contact and ingestion and its sale, strength, and labeling are regulated in most jurisdictions. Handle and store it accordingly, and follow the rules that apply where you are.