To make 820 rune bars at the Blast Furnace in Old School RuneScape, you’ll need 820 rune ores and 3,280 coal (because rune bars require an 8:1 coal-to-ore ratio, and the Blast Furnace halves the coal needed).

How the math works

Standard smelting ratio for rune bars

  • Normally, 1 rune bar = 1 rune ore + 8 coal.

Blast Furnace effect

  • The Blast Furnace halves the coal requirement for smelting bars.
  • So at the Blast Furnace:
    1 rune bar = 1 rune ore + 4 coal

Calculation for 820 rune bars

  • Rune ore needed: 820 × 1 = 820 rune ores
  • Coal needed: 820 × 4 = 3,280 coal

TL;DR: 820 rune ores + 3,280 coal → 820 rune bars at the Blast Furnace.

Practical tips for efficient runs

If you’re batching this over multiple trips, here’s a common setup many players use:

  • Use a coal bag to carry extra coal per trip.
  • Typical efficient cycle:
    1. Bring 2 inventories of coal + fill coal bag.
    2. Deposit coal at the conveyor belt.
    3. Bring rune ore + more coal (or just ore if you’ve stockpiled enough coal).
    4. Smelt, collect bars, repeat.

This minimizes back-and-forth while keeping the furnace fed.

Sources

Information gathered from public forums or data available on the internet and portrayed here.