---
title: "Calculate Transaction Mass"
method: POST
path: "/transactions/mass"
tags: ["Kaspa transactions"]
---

# Calculate Transaction Mass

`POST /transactions/mass`

This function calculates and returns the mass of a transaction, which is essential for determining the minimum fee. The mass calculation takes into account the storage mass as defined in KIP-0009.

Note: Be aware that if the transaction has a very low output amount or a high number of outputs, the mass can become significantly large.

## Request body

- SubmitTxModel
  - `version` integer, required
  - `inputs` SubmitTxInput[], required
    - `previousOutpoint` SubmitTxOutpoint, required
      - `transactionId` string, required
      - `index` integer, required
    - `signatureScript` string, required
    - `sequence` integer, required
    - `sigOpCount` integer, required
  - `outputs` SubmitTxOutput[], required
    - `amount` integer, required
    - `scriptPublicKey` SubmitTxScriptPublicKey, required
      - `version` integer, required
      - `scriptPublicKey` string, required
  - `lockTime` integer
  - `subnetworkId` string

## Response `200`

Successful Response

- TxMass
  - `mass` integer, required
  - `storage_mass` integer, required
  - `compute_mass` integer, required

## Other responses

- `422` — Validation Error

---

[API](https://skmtc.dev/kaspa/apis/kaspa-rest-api-server.md) · [All operations](https://skmtc.dev/kaspa/apis/kaspa-rest-api-server/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/kaspa/kaspa-rest-api-server/revisions/12089df981aa/schema)