OSRS Gemstone Crab Calculator

Combat experience an hour at the Gemstone Crab for every recommended weapon, time and crabs to your goal, ammunition and rune costs, and the gems each shell gives.

Prices updated just now · Tool added 25 Oct 2026

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Attack

Strength

Defence

Ranged

Magic

Hitpoints

Prayer

Combat style

Experience to

Weapon

Armour set

Attack bonus

Strength bonus

From the rest of your equipment: everything except the weapon, its ammunition and the set above.

Boost

Prayer

Goal level

Seconds lost a move

You are in the top 16 for damage, so you mine the shell

XP an hour—

Time to your goal—

Crabs—

Max hit—

Experience an hour

Experience an hour at the crab and the time to your goal, skill by skill
Skill	Level	XP an hour	Time to goal

Supplies and gems an hour

What the method uses and earns an hour
Item	An hour	Coins

Every weapon side by side

Your levels, boost, prayer and other gear with each weapon the crab's guide recommends.

Experience an hour and supplies with every weapon for this style
Weapon	Max hit	Accuracy	XP an hour	Supplies an hour

Every spell side by side

Every elemental combat spell, cast with the staff above. Spells above your Magic level are greyed out.

Experience an hour and runes with every combat spell
Spell	Max hit	XP an hour	Runes an hour

Gems from the shell

Each gem the shell gives, how often, and what it is worth
Gem	A crab	An hour	Each	Crafting XP to cut

Hits follow the game's combat formulas. The crab has 1 in every combat stat and no defence bonus, so each weapon's max hit, accuracy and attack speed decide the rate, and every point of damage gives 12.5% less experience than usual: 3.5 a damage in place of 4. A successful hit of 0 counts as 1, and nothing is lost to overkill. Time at the crab is an estimate: about 10 minutes a crab and 30 seconds lost each time it moves, marked with a ~. Type your own seconds above. Costs use today's instant-buy prices and gems today's instant-sell prices after the 2% tax; potions and prayer are not counted. Rules checked against the OSRS Wiki on 25 October 2026.

How the Gemstone Crab works

The Gemstone Crab is a world boss in the Tlati Rainforest, and the only thing you need to fight it is Children of the Sun. It moves between three mines about every 10 minutes. Its health bar is a timer, not a measure of your damage, so it never dies under you and you never wait for a respawn. When it burrows, the cave at any of the three mines takes you to where it went next. It has 1 in every combat stat and no defence bonus, which is why accuracy barely matters and damage is what to raise.

Every hit gives 12.5% less combat and Hitpoints experience than the same hit on most monsters. It still tends to beat sand and rock crabs, because you are never out of combat and no damage is wasted on a monster with 1 Hitpoint left. The crab can hit back for 1 at the players it faces, so a hardcore ironman should not sit at low Hitpoints.

Gems from the shell

When the crab burrows it leaves a piece of shell for 90 seconds. The 16 players who dealt it the most damage can mine it with any pickaxe for 3 uncut gems, rolled from this table each time. Mining it needs no Mining level and gives no Mining experience.

Each gem the shell can give and its chance on one roll
Gem	Chance a roll
Uncut opal	9/32
Uncut jade	9/32
Uncut red topaz	6/32
Uncut sapphire	3/32
Uncut emerald	2/32
Uncut ruby	2/32
Uncut diamond	1/32
Uncut dragonstone	1/500

The seven 32nds already add up to one, so the page counts the dragonstone as a 1 in 500 check first and the other seven share what is left. Over a long session that is 17.1 gems an hour.

Magic between hits

Combat spells are a slow way to train Magic at the crab: it has no elemental weakness and the 12.5% cut applies to the damage. The crab's guide suggests training Melee or Ranged on it and casting something else between hits, at these rates:

Magic experience an hour from spells cast between hits
Spell	Magic XP an hour	How
High Level Alchemy	78,000	Cast between hits on every attack, 1,200 casts an hour at 65 experience.
Telekinetic Grab	~125,000	Picking up the ammunition other players leave under the crab, on a busy world. The page says upwards of about 125,000.
Magic Imbue	24,500	86 experience every 12.6 seconds on the Lunar spellbook.

Ranged ammunition

Darts are the cheap choice before 46 Ranged; from 46 an adamant crossbow with ruby bolts (e) is strong, because the bolt's effect hits for 60 and the crab counts as having 300 Hitpoints for it. The hard Kandarin Diary makes the effect fire more often, and the achievement diaries calculator lists every task it needs. With an Ava's device most ammunition comes back: the attractor loses 2 shots in 5, the accumulator 7 in 25 and the assembler 1 in 5. The Ranged calculator lists the crab with mithril darts beside every other way to train, and the DPS calculator takes your whole loadout against any other monster.

Update history

Every change to this calculator

25 Oct 2026 Calculator added