Gravity & Volume Correction Calculator
Adjust gravity for a volume change - boil-off concentration, top-up, or pre-boil to post-boil.
Measured now, e.g. 1.040
Volume at the current gravity
Same unit as above
1.049 SG
What happensconcentrated (boil-off)
How it works
Use this for boil-off concentration, top-up dilution, or converting a pre-boil reading to a post-boil one. Only water is assumed to enter or leave, so the wort's sugar - its gravity points - is conserved. Reduce the volume and gravity rises; increase the volume and it falls.
gravity points × volume = constant
newSG points = currentSG points × (currentVolume / newVolume)
Sources: standard gravity-points conservation, as documented by Brewer's Friend.
Assumes pure water is gained or lost. Real boils also lose a little sugar to trub and hop absorption, so expect the measured gravity to land slightly under the prediction.
Frequently asked questions
- How does gravity change when I boil off or top up wort?
- Sugar (gravity points) is conserved when only water leaves or is added. Boiling off water concentrates the wort, raising gravity; adding water dilutes it, lowering gravity. Gravity points × volume stays constant, so the new gravity is the old points scaled by the volume ratio.
- Can I use this for pre-boil to post-boil gravity?
- Yes. Enter your measured pre-boil gravity and pre-boil volume as the current values and your expected post-boil volume as the target - the result is your predicted post-boil gravity.
- Does this account for sugar lost to trub or hops?
- No. It assumes only water enters or leaves. Small losses to hop and break material slightly reduce real-world gravity, so treat the result as a close planning estimate.