EVE Online gas huffing calculator

Pick the ship and the scoops you fly and see which cloud pays best - per hour, at the market you sell to, with the residue each one burns.

How gas harvesting is worked out

Scoops on frigates and destroyers, harvesters on barges. A Venture or Prospect doubles scoop yield and Mining Frigate cuts the cycle by 5% a level; barges and exhumers cut harvester cycles instead.
Gas Cloud Harvesting allows one module per level - the calculator will not let you fit a third scoop with the skill at II.
No critical successes. The Catalyst crit mechanic does not apply to gas, so the yield per cycle is exactly what the module pulls.
Residue matters in wormholes. A Gas Cloud Scoop II wastes as much gas as it harvests in about a third of its cycles - your hold does not notice, the site does. The Syndicate and ORE modules waste nothing.
Boosts and implants - the Mining Laser Optimization burst shortens gas cycles just like ore cycles, and the Eifyr and Co. 'Alchemist' implants take another 1-5% off.

What it does not include

Travel and scanning time are left out, and so is the danger: sleepers arrive in wormhole gas sites after a while, and some cytoserocin clouds damage your ship each cycle. Prices come from one market - booster gas often sells better as a finished booster, which the production chain can price for you. Ore has its own calculator.