diff --git a/specs/phase1/beacon-chain.md b/specs/phase1/beacon-chain.md
index aa3d3e2c9..b49fb00f3 100644
--- a/specs/phase1/beacon-chain.md
+++ b/specs/phase1/beacon-chain.md
@@ -76,6 +76,8 @@ We define the following Python custom types for type hinting and readability:
 | `MAX_SHARD_HEADERS_PER_SHARD` | `4` | |
 | `MAX_SHARD_HEADERS` | `MAX_SHARDS * MAX_SHARD_HEADERS_PER_SHARD` | |
 | `PRIMITIVE_ROOT_OF_UNITY` | `5` | Primitive root of unity of the BLS12_381 (inner) modulus |
+| `DATA_AVAILABILITY_INVERSE_CODING_RATE` | `2**1` (=2) | Factor by which samples are extended for data availability encoding |
+
 
 ### Shard block configs
 
@@ -93,7 +95,7 @@ We define the following Python custom types for type hinting and readability:
 | `ROOT_OF_UNITY` | `pow(PRIMITIVE_ROOT_OF_UNITY, (MODULUS - 1) // (MAX_SAMPLES_PER_BLOCK * POINTS_PER_SAMPLE, MODULUS)` | |
 | `SIZE_CHECK_POINTS` | Type `List[G2, MAX_SAMPLES_PER_BLOCK + 1]`; TO BE COMPUTED |
 
-These points are the G2-side Kate commitments to `product[a in i...MAX_SAMPLES_PER_BLOCK-1] (X ** POINTS_PER_SAMPLE - w ** (reverse_bit_order(a, MAX_SAMPLES_PER_BLOCK * 2) * POINTS_PER_SAMPLE))` for each `i` in `[0...MAX_SAMPLES_PER_BLOCK]`, where `w = ROOT_OF_UNITY`. They are used to verify block size proofs. They can be computed with a one-time O(N^2/log(N)) calculation using fast-linear-combinations in G2.
+These points are the G2-side Kate commitments to `product[a in i...MAX_SAMPLES_PER_BLOCK-1] (X ** POINTS_PER_SAMPLE - w ** (reverse_bit_order(a, MAX_SAMPLES_PER_BLOCK * DATA_AVAILABILITY_INVERSE_CODING_RATE) * POINTS_PER_SAMPLE))` for each `i` in `[0...MAX_SAMPLES_PER_BLOCK]`, where `w = ROOT_OF_UNITY`. They are used to verify block size proofs. They can be computed with a one-time O(N^2/log(N)) calculation using fast-linear-combinations in G2.
 
 ### Gwei values