Gemstone Crab Calculator
Equip any item from the OSRS Wiki, choose your prayer and potion, and see your accuracy, max hit and damage per hour against the Gemstone Crab. Set a target level and the calculator works out how long you need to spend at the crab to reach it, including the crab's 12.5% XP penalty.
Your combat setup
Your stats Enter a level or your exact XP
Equipment Click a slot to search and equip an item
Combat options
Training goal Time and kills until your target
Breakdown
| XP type | XP/hour |
|---|
How the Gemstone Crab calculator works
This calculator works out your accuracy, max hit and XP per hour against the Gemstone Crab from the gear, prayer, potion and attack style you pick, then tells you how long you need to spend at the crab to reach a target level. Item stats are read live from the OSRS Wiki, so new gear shows up automatically.
Quick facts
- You need membership and completion of Children of the Sun to reach Varlamore. There is no combat level requirement.
- The crab is in the Tlati Rainforest and moves between three spawn points roughly every 10 minutes.
- It has combat level 160, attacks with crush every 7 ticks (4.2 seconds) and never hits for more than 1.
- Every defensive bonus is +0 and its defence level is 1, so accuracy is close to 100% for almost any build. Damage per hit and attack speed are what matter.
- Combat XP is 87.5% of normal (a 12.5% reduction), but no XP is lost to overkill and there is almost no downtime between hits.
- It does not count as a Slayer task monster, so Slayer helmet bonuses do not apply. It is immune to poison, venom, cannons, thralls, burn and freeze.
- After the fight, the top 16 players by damage dealt get a 90-second window to mine the shell with a pickaxe and receive 3 random uncut gems (opal up to dragonstone). Dragonstones are rare.
Tips
- Melee is the most effective style overall. Put strength bonus ahead of accuracy, since the crab cannot dodge.
- Ranged is worthwhile at lower levels: darts before level 46, then an adamant crossbow with ruby bolts (e) until roughly level 65 to 70. Use the Rapid style for speed.
- Magic is much less recommended and is inefficient at every level, so use the calculator to compare it against melee and ranged for your own setup.
- Low-level prayers such as Burst of Strength drain very slowly while raising your max hit.
- Bring a pickaxe so you can mine the shell afterwards. Because eligibility is decided by damage dealt, staying on the crab for the whole fight helps.
Frequently asked questions
How does the calculator work out time to my target level?
It takes the XP you still need and divides it by your XP per hour. XP per hour comes from your average damage per hit, your weapon's attack speed and the crab's 12.5% XP reduction.
Why is my accuracy almost always near 100%?
The crab has defence level 1 and +0 in every defence bonus, so even a modest attack roll almost always hits. That is why the calculator focuses on max hit and attack speed.
How much XP do I get per point of damage?
Melee and ranged give 4 XP per point of damage (3.5 after the crab's reduction). Magic gives 2 per point plus each spell's own cast XP, and you also gain Hitpoints XP on top.
Do my choices survive a page refresh?
Yes. Your gear, levels, attack style, prayer, potion and spell are saved in your own browser only and restored when you come back. Nothing is sent to a server.
Facts checked against the OSRS Wiki in September 2026. Game mechanics and prices can change with updates, so double-check important decisions in the game.