In most cases, 1 - 250ml adhesive cartridge will produce a 40 ft 1/4' bead. As each project has different needs you will need to calculate your own specific needs. As a rule of thumb if you are coming close to needing another cartridge, you should order another one to protect against design changes, dispensing larger than 1/4" beads and calculation errors. Several tips per cartridge are usually needed. You should only glue as much material together at a time as you can easily place and clamp. Each time you set the adhesive gun aside for 15-20 minutes the glue in the tip of the mixing tube will harden and you will need a new tip when you dispense adhesive again. Leaving the mixing tip in place with the hardened end is good as it keeps the adhesive in the cartridge fresh and away from air.