Page Speed Budget
Free Page Speed Budget calculator with clear step-by-step results.
About Page Speed Budget
Derives a byte budget from a load-time target rather than picking a round number. Connection setup costs about three round trips, requests queue in parallel batches that each cost a round trip, and rendering consumes real time - whatever is left is what you can spend on bytes.
Formulas
Overhead
Overhead = 3 x RTT + ceil(requests / 6) x RTT + render time
Byte budget
KB = (target - overhead) x Mbps x 1000 / 8
Worked example
With the default values below, Page Speed Budget returns Page weight budget of 550.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Target load timeminimum 0.2 s
- 3 s
- Target connection speedminimum 0.1 Mbps
- 5 Mbps
- Round trip latencyminimum 1 ms
- 120 ms
- Number of requestsminimum 1
- 45
- Time spent parsing and renderingminimum 0 s
- 0.8 s
Results
- Page weight budget
- 550.0 KB
- Time left for transferring bytes
- 0.880 s
- Latency and rendering overhead
- 2.120 s
- Average budget per request
- 12.22 KB
Step by step
- 1Values used
- 2Overhead
- 3Byte budget
- 4Page weight budget= 550.0 KB
- 5Time left for transferring bytes= 0.880 s
- 6Latency and rendering overhead= 2.120 s
- 7Average budget per request= 12.22 KB
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why is the budget so small on slow connections?
Because latency eats the budget before any bytes move. On a 120 ms RTT, connection setup and request batching alone can consume over a second regardless of bandwidth.
What if the budget comes out negative?
The target is unreachable at that latency and request count. Reduce requests, use HTTP/2 or HTTP/3 multiplexing, or cut render-blocking work before worrying about file sizes.